uspas course on recirculated and energy recovered linacs g. a. krafft and a. bogacz jefferson lab...
TRANSCRIPT
USPAS Course onRecirculated and Energy Recovered Linacs
G A Krafft and A Bogacz
Jefferson Lab
Timofey Zolkin
Lecture 12 ERL x-ray light source
USPAS Accelerator Physics June 2013
High Field Spectral Distribution
02222
2
20
2 sin
2
nxnnperp n
c
e
dd
dE
02
2
2
1
22
20
2
cos
sin
sin
cos
sin
cos
2
n
z
n
n
npar
n
S
S
nc
e
dd
dE
(216)
In the beam frame
where
00
00100 sin
sin
nn
nnNnfnfnNn
USPAS Accelerator Physics June 2013
In the lab frame
nfnS
S
c
e
dd
dE
nNn
n
z
z
nperp
sin
cossin
cos1
cos1
1
2
22
2
2
1
22
22
22
2
nf
n
S
S
c
e
dd
dEnN
zn
zn
z
npar
cossin
cos1sin
cos
cos1
1
22
2
2
1
22
2
0
0
cos1sin
cos1sin
n
nnNnf
zz
zznN
USPAS Accelerator Physics June 2013
nfnSSc
e
dd
dEnNnn
nperp cossin
sin
22
22
22
21
2
nf
n
S
S
c
e
dd
dEnN
n
z
zn
npar
cossin
sincos1
cos
22
2
2
12
fnN is highly peaked with peak value nN around angular frequency
0 as 21
22
cos1
02
2
020
n
Kn
nn z
z
z
USPAS Accelerator Physics June 2013
Energy Distribution in Lab Frame
nfnSSc
e
dd
dEnNnn
nperp cossin
sin
22
22
22
21
2
nf
n
S
S
c
e
dd
dEnN
n
z
zn
npar
cossin
sincos1
cos
22
2
2
12
The arguments of the Bessel Functions are now
22
2
0
0
8
cos1
coscos
cos1
cossincossin
Kncdn
Kncdn
z
zzzz
zxx
(217)
USPAS Accelerator Physics June 2013
In the Forward DirectionIn the forward direction even harmonics vanish (n+2krsquo term vanishes when ldquoxrdquo Bessel function non-zero at zero argument and all other terms in sum vanish with a power higher than 2 as the argument goes to zero) and for odd harmonics only n+2krsquo=1-1 contribute to the sum
0 sin2
222
22
nf
n
KF
c
e
dd
dEnN
nnperp
0 cos2
222
22
nf
n
KF
c
e
dd
dEnN
nnpar
2
2
2
2
12
2
2
12
2
2
2
2 21421414
1
K
nKJ
K
nKJ
KnKF nn
z
n
USPAS Accelerator Physics June 2013
Number Spectral Angular Density
0 sin
22
22
nf
n
KF
dd
dNnN
nnperp
0 cos
22
22
nf
n
KF
dd
dNnN
nnpar
Converting the energy density into an number density by dividing by the photon energy (donrsquot forget both signs of frequency)
KFNdd
dNn
ntot 22
Peak value in the forward direction
USPAS Accelerator Physics June 2013
Radiation Pattern Qualitatively
Central cone high angular density region around forward direction
y
x
Central Cone
Doppler DownshiftedHarmonic Radiation
Non-zero AngularDensity Emission ata Given Frequency
r
1n
1l
2l
USPAS Accelerator Physics June 2013
Dimension Estimates
Harmonic bands at
211 2K
n
lnl
Central cone size estimated by requiring Gaussian distribution with correct peak value integrate over solid angle to the same number of total photons as integrating f
0 2
21
2
1 2
ncLnN
Kn
nr
Much narrower than typical opening angle for bend
USPAS Accelerator Physics June 2013
Number Spectral Density (Flux)
The flux in the central cone is obtained by estimating solid angle integral by the peak angular density multiplied by the Gaussian integral
Kge
IN n
nF
nKFKKg nn 21 2
2
0
n 2F rntot
d
dN
USPAS Accelerator Physics June 2013
Power Angular Density
22
22
21
cossin
sin nSSNn
d
dEnn
nperp
2
2
1
cossin
sincos1
cos
n
S
S
Nnd
dE
n
z
zn
npar
Donrsquot forget both signs of frequency
USPAS Accelerator Physics June 2013
2
2
22
222
coscos1
cos
cos14
sincos14
z
z
z
nparn
z
nperpn
KNF
d
dN
KNF
d
dN
2
2
2
2
12
2
2
122
22
21421421
K
nKJ
K
nKJ
K
KnKF nnn
For K less than or of order one
Compare with (210)
USPAS Accelerator Physics June 2013
USPAS Accelerator Physics June 2013
ERL light source ideaThird generation light sources are storage ring based facilities
optimized for production of high brilliance x-rays through spontaneous synchrotron radiation The technology is mature and while some improvement in the future is likely one ought to ask whether an alternative approach exists
Two orthogonal ideas (both linac based) are XFEL and ERL XFEL will not be spontaneous synchrotron radiation source but will deliver GW peak powers of transversely coherent radiation at very low duty factor The source parameters are very interesting and at the same time very different from any existing light source
ERL aspires to do better what storage rings are very good at to provide radiation in quasi-continuous fashion with superior brilliance monochromaticity and shorter pulses
USPAS Accelerator Physics June 2013
Coherent or incoherent
Radiation field from a single kth electron in a bunch
Radiation field from the whole bunch bunching factor (bf)
Radiation Intensity
1) ldquolong bunchrdquo =gt incoherent (conventional) SR
2) ldquoshort bunchrdquo or -bunching =gt coherent (FELs) SR
ERL hard x-ray source is envisioned to use conventional SR
)exp(0 kk tiEE
eN
kk
e
tiN
fb1
)exp(1
22
0 eNfbII
single electron
eNfb 1~2
eNII 0
1 fb 20~ eNII
USPAS Accelerator Physics June 2013
Demand for X-rays
~85 structures by ~85 structures by x-ray crystallographyx-ray crystallography
2003 Nobel Prize 2003 Nobel Prize in Chemistryin Chemistry
Roderick MacKinnonRoderick MacKinnon (Rockefeller Univ)(Rockefeller Univ)
11stst K K++ channel structure channel structure by x-ray crystallography by x-ray crystallography
based on CHESS data (1998)based on CHESS data (1998)
Ion channel proteinIon channel protein
CHESSCHESS
USPAS Accelerator Physics June 2013
X-ray characteristics neededbull for properly tuned undulator X-ray phase space is a replica from electron bunch + convolution with the diffraction limit
bull ideally one wants the phase space to be diffraction limited (ie full transverse coherence) eg rms = 4 or 01 Aring for 8 keV X-rays (Cu K) or01 m normalized at 5 GeV
Flux phs01bw
Brightness phsmrad201bw
Brilliance phsmm2mrad201bw
USPAS Accelerator Physics June 2013
Introduction
6D Phase Space Area6D Phase Space Areandash Horizontal Emittance x xrsquondash Vertical Emittance y yrsquondash Energy Spread amp Bunch length
ΔE t
Number of Electrons BunchNumber of Electrons BunchBunch Rep RateBunch Rep Rate IIpeakpeak I Iaverageaverage
Letrsquos review why ERL is a good idea for a light sourceLetrsquos review why ERL is a good idea for a light source
Critical electron beam parameters for X-ray productionCritical electron beam parameters for X-ray production
USPAS Accelerator Physics June 2013
Introduction (contd) adiabatic damping px
p1z
p1
θ1x
electron bunch ε1
linac
px p2
p2z
θ2x
ε2 = ε1 p2z p1z
ε = εn
βγ εn is invariant since
x px = mc2βγθx form canonically conjugate variables
geometricx θx
mc2
normalized x px
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (I)
Quantum Excitation
ρ = p
eB ρ =
p eB p
eB
Equilibrium
Eph
22
~ phphE EN
dt
d
Radiative Dampingvs
Emittance (hor) Energy Spread Bunch Length
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
High Field Spectral Distribution
02222
2
20
2 sin
2
nxnnperp n
c
e
dd
dE
02
2
2
1
22
20
2
cos
sin
sin
cos
sin
cos
2
n
z
n
n
npar
n
S
S
nc
e
dd
dE
(216)
In the beam frame
where
00
00100 sin
sin
nn
nnNnfnfnNn
USPAS Accelerator Physics June 2013
In the lab frame
nfnS
S
c
e
dd
dE
nNn
n
z
z
nperp
sin
cossin
cos1
cos1
1
2
22
2
2
1
22
22
22
2
nf
n
S
S
c
e
dd
dEnN
zn
zn
z
npar
cossin
cos1sin
cos
cos1
1
22
2
2
1
22
2
0
0
cos1sin
cos1sin
n
nnNnf
zz
zznN
USPAS Accelerator Physics June 2013
nfnSSc
e
dd
dEnNnn
nperp cossin
sin
22
22
22
21
2
nf
n
S
S
c
e
dd
dEnN
n
z
zn
npar
cossin
sincos1
cos
22
2
2
12
fnN is highly peaked with peak value nN around angular frequency
0 as 21
22
cos1
02
2
020
n
Kn
nn z
z
z
USPAS Accelerator Physics June 2013
Energy Distribution in Lab Frame
nfnSSc
e
dd
dEnNnn
nperp cossin
sin
22
22
22
21
2
nf
n
S
S
c
e
dd
dEnN
n
z
zn
npar
cossin
sincos1
cos
22
2
2
12
The arguments of the Bessel Functions are now
22
2
0
0
8
cos1
coscos
cos1
cossincossin
Kncdn
Kncdn
z
zzzz
zxx
(217)
USPAS Accelerator Physics June 2013
In the Forward DirectionIn the forward direction even harmonics vanish (n+2krsquo term vanishes when ldquoxrdquo Bessel function non-zero at zero argument and all other terms in sum vanish with a power higher than 2 as the argument goes to zero) and for odd harmonics only n+2krsquo=1-1 contribute to the sum
0 sin2
222
22
nf
n
KF
c
e
dd
dEnN
nnperp
0 cos2
222
22
nf
n
KF
c
e
dd
dEnN
nnpar
2
2
2
2
12
2
2
12
2
2
2
2 21421414
1
K
nKJ
K
nKJ
KnKF nn
z
n
USPAS Accelerator Physics June 2013
Number Spectral Angular Density
0 sin
22
22
nf
n
KF
dd
dNnN
nnperp
0 cos
22
22
nf
n
KF
dd
dNnN
nnpar
Converting the energy density into an number density by dividing by the photon energy (donrsquot forget both signs of frequency)
KFNdd
dNn
ntot 22
Peak value in the forward direction
USPAS Accelerator Physics June 2013
Radiation Pattern Qualitatively
Central cone high angular density region around forward direction
y
x
Central Cone
Doppler DownshiftedHarmonic Radiation
Non-zero AngularDensity Emission ata Given Frequency
r
1n
1l
2l
USPAS Accelerator Physics June 2013
Dimension Estimates
Harmonic bands at
211 2K
n
lnl
Central cone size estimated by requiring Gaussian distribution with correct peak value integrate over solid angle to the same number of total photons as integrating f
0 2
21
2
1 2
ncLnN
Kn
nr
Much narrower than typical opening angle for bend
USPAS Accelerator Physics June 2013
Number Spectral Density (Flux)
The flux in the central cone is obtained by estimating solid angle integral by the peak angular density multiplied by the Gaussian integral
Kge
IN n
nF
nKFKKg nn 21 2
2
0
n 2F rntot
d
dN
USPAS Accelerator Physics June 2013
Power Angular Density
22
22
21
cossin
sin nSSNn
d
dEnn
nperp
2
2
1
cossin
sincos1
cos
n
S
S
Nnd
dE
n
z
zn
npar
Donrsquot forget both signs of frequency
USPAS Accelerator Physics June 2013
2
2
22
222
coscos1
cos
cos14
sincos14
z
z
z
nparn
z
nperpn
KNF
d
dN
KNF
d
dN
2
2
2
2
12
2
2
122
22
21421421
K
nKJ
K
nKJ
K
KnKF nnn
For K less than or of order one
Compare with (210)
USPAS Accelerator Physics June 2013
USPAS Accelerator Physics June 2013
ERL light source ideaThird generation light sources are storage ring based facilities
optimized for production of high brilliance x-rays through spontaneous synchrotron radiation The technology is mature and while some improvement in the future is likely one ought to ask whether an alternative approach exists
Two orthogonal ideas (both linac based) are XFEL and ERL XFEL will not be spontaneous synchrotron radiation source but will deliver GW peak powers of transversely coherent radiation at very low duty factor The source parameters are very interesting and at the same time very different from any existing light source
ERL aspires to do better what storage rings are very good at to provide radiation in quasi-continuous fashion with superior brilliance monochromaticity and shorter pulses
USPAS Accelerator Physics June 2013
Coherent or incoherent
Radiation field from a single kth electron in a bunch
Radiation field from the whole bunch bunching factor (bf)
Radiation Intensity
1) ldquolong bunchrdquo =gt incoherent (conventional) SR
2) ldquoshort bunchrdquo or -bunching =gt coherent (FELs) SR
ERL hard x-ray source is envisioned to use conventional SR
)exp(0 kk tiEE
eN
kk
e
tiN
fb1
)exp(1
22
0 eNfbII
single electron
eNfb 1~2
eNII 0
1 fb 20~ eNII
USPAS Accelerator Physics June 2013
Demand for X-rays
~85 structures by ~85 structures by x-ray crystallographyx-ray crystallography
2003 Nobel Prize 2003 Nobel Prize in Chemistryin Chemistry
Roderick MacKinnonRoderick MacKinnon (Rockefeller Univ)(Rockefeller Univ)
11stst K K++ channel structure channel structure by x-ray crystallography by x-ray crystallography
based on CHESS data (1998)based on CHESS data (1998)
Ion channel proteinIon channel protein
CHESSCHESS
USPAS Accelerator Physics June 2013
X-ray characteristics neededbull for properly tuned undulator X-ray phase space is a replica from electron bunch + convolution with the diffraction limit
bull ideally one wants the phase space to be diffraction limited (ie full transverse coherence) eg rms = 4 or 01 Aring for 8 keV X-rays (Cu K) or01 m normalized at 5 GeV
Flux phs01bw
Brightness phsmrad201bw
Brilliance phsmm2mrad201bw
USPAS Accelerator Physics June 2013
Introduction
6D Phase Space Area6D Phase Space Areandash Horizontal Emittance x xrsquondash Vertical Emittance y yrsquondash Energy Spread amp Bunch length
ΔE t
Number of Electrons BunchNumber of Electrons BunchBunch Rep RateBunch Rep Rate IIpeakpeak I Iaverageaverage
Letrsquos review why ERL is a good idea for a light sourceLetrsquos review why ERL is a good idea for a light source
Critical electron beam parameters for X-ray productionCritical electron beam parameters for X-ray production
USPAS Accelerator Physics June 2013
Introduction (contd) adiabatic damping px
p1z
p1
θ1x
electron bunch ε1
linac
px p2
p2z
θ2x
ε2 = ε1 p2z p1z
ε = εn
βγ εn is invariant since
x px = mc2βγθx form canonically conjugate variables
geometricx θx
mc2
normalized x px
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (I)
Quantum Excitation
ρ = p
eB ρ =
p eB p
eB
Equilibrium
Eph
22
~ phphE EN
dt
d
Radiative Dampingvs
Emittance (hor) Energy Spread Bunch Length
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
In the lab frame
nfnS
S
c
e
dd
dE
nNn
n
z
z
nperp
sin
cossin
cos1
cos1
1
2
22
2
2
1
22
22
22
2
nf
n
S
S
c
e
dd
dEnN
zn
zn
z
npar
cossin
cos1sin
cos
cos1
1
22
2
2
1
22
2
0
0
cos1sin
cos1sin
n
nnNnf
zz
zznN
USPAS Accelerator Physics June 2013
nfnSSc
e
dd
dEnNnn
nperp cossin
sin
22
22
22
21
2
nf
n
S
S
c
e
dd
dEnN
n
z
zn
npar
cossin
sincos1
cos
22
2
2
12
fnN is highly peaked with peak value nN around angular frequency
0 as 21
22
cos1
02
2
020
n
Kn
nn z
z
z
USPAS Accelerator Physics June 2013
Energy Distribution in Lab Frame
nfnSSc
e
dd
dEnNnn
nperp cossin
sin
22
22
22
21
2
nf
n
S
S
c
e
dd
dEnN
n
z
zn
npar
cossin
sincos1
cos
22
2
2
12
The arguments of the Bessel Functions are now
22
2
0
0
8
cos1
coscos
cos1
cossincossin
Kncdn
Kncdn
z
zzzz
zxx
(217)
USPAS Accelerator Physics June 2013
In the Forward DirectionIn the forward direction even harmonics vanish (n+2krsquo term vanishes when ldquoxrdquo Bessel function non-zero at zero argument and all other terms in sum vanish with a power higher than 2 as the argument goes to zero) and for odd harmonics only n+2krsquo=1-1 contribute to the sum
0 sin2
222
22
nf
n
KF
c
e
dd
dEnN
nnperp
0 cos2
222
22
nf
n
KF
c
e
dd
dEnN
nnpar
2
2
2
2
12
2
2
12
2
2
2
2 21421414
1
K
nKJ
K
nKJ
KnKF nn
z
n
USPAS Accelerator Physics June 2013
Number Spectral Angular Density
0 sin
22
22
nf
n
KF
dd
dNnN
nnperp
0 cos
22
22
nf
n
KF
dd
dNnN
nnpar
Converting the energy density into an number density by dividing by the photon energy (donrsquot forget both signs of frequency)
KFNdd
dNn
ntot 22
Peak value in the forward direction
USPAS Accelerator Physics June 2013
Radiation Pattern Qualitatively
Central cone high angular density region around forward direction
y
x
Central Cone
Doppler DownshiftedHarmonic Radiation
Non-zero AngularDensity Emission ata Given Frequency
r
1n
1l
2l
USPAS Accelerator Physics June 2013
Dimension Estimates
Harmonic bands at
211 2K
n
lnl
Central cone size estimated by requiring Gaussian distribution with correct peak value integrate over solid angle to the same number of total photons as integrating f
0 2
21
2
1 2
ncLnN
Kn
nr
Much narrower than typical opening angle for bend
USPAS Accelerator Physics June 2013
Number Spectral Density (Flux)
The flux in the central cone is obtained by estimating solid angle integral by the peak angular density multiplied by the Gaussian integral
Kge
IN n
nF
nKFKKg nn 21 2
2
0
n 2F rntot
d
dN
USPAS Accelerator Physics June 2013
Power Angular Density
22
22
21
cossin
sin nSSNn
d
dEnn
nperp
2
2
1
cossin
sincos1
cos
n
S
S
Nnd
dE
n
z
zn
npar
Donrsquot forget both signs of frequency
USPAS Accelerator Physics June 2013
2
2
22
222
coscos1
cos
cos14
sincos14
z
z
z
nparn
z
nperpn
KNF
d
dN
KNF
d
dN
2
2
2
2
12
2
2
122
22
21421421
K
nKJ
K
nKJ
K
KnKF nnn
For K less than or of order one
Compare with (210)
USPAS Accelerator Physics June 2013
USPAS Accelerator Physics June 2013
ERL light source ideaThird generation light sources are storage ring based facilities
optimized for production of high brilliance x-rays through spontaneous synchrotron radiation The technology is mature and while some improvement in the future is likely one ought to ask whether an alternative approach exists
Two orthogonal ideas (both linac based) are XFEL and ERL XFEL will not be spontaneous synchrotron radiation source but will deliver GW peak powers of transversely coherent radiation at very low duty factor The source parameters are very interesting and at the same time very different from any existing light source
ERL aspires to do better what storage rings are very good at to provide radiation in quasi-continuous fashion with superior brilliance monochromaticity and shorter pulses
USPAS Accelerator Physics June 2013
Coherent or incoherent
Radiation field from a single kth electron in a bunch
Radiation field from the whole bunch bunching factor (bf)
Radiation Intensity
1) ldquolong bunchrdquo =gt incoherent (conventional) SR
2) ldquoshort bunchrdquo or -bunching =gt coherent (FELs) SR
ERL hard x-ray source is envisioned to use conventional SR
)exp(0 kk tiEE
eN
kk
e
tiN
fb1
)exp(1
22
0 eNfbII
single electron
eNfb 1~2
eNII 0
1 fb 20~ eNII
USPAS Accelerator Physics June 2013
Demand for X-rays
~85 structures by ~85 structures by x-ray crystallographyx-ray crystallography
2003 Nobel Prize 2003 Nobel Prize in Chemistryin Chemistry
Roderick MacKinnonRoderick MacKinnon (Rockefeller Univ)(Rockefeller Univ)
11stst K K++ channel structure channel structure by x-ray crystallography by x-ray crystallography
based on CHESS data (1998)based on CHESS data (1998)
Ion channel proteinIon channel protein
CHESSCHESS
USPAS Accelerator Physics June 2013
X-ray characteristics neededbull for properly tuned undulator X-ray phase space is a replica from electron bunch + convolution with the diffraction limit
bull ideally one wants the phase space to be diffraction limited (ie full transverse coherence) eg rms = 4 or 01 Aring for 8 keV X-rays (Cu K) or01 m normalized at 5 GeV
Flux phs01bw
Brightness phsmrad201bw
Brilliance phsmm2mrad201bw
USPAS Accelerator Physics June 2013
Introduction
6D Phase Space Area6D Phase Space Areandash Horizontal Emittance x xrsquondash Vertical Emittance y yrsquondash Energy Spread amp Bunch length
ΔE t
Number of Electrons BunchNumber of Electrons BunchBunch Rep RateBunch Rep Rate IIpeakpeak I Iaverageaverage
Letrsquos review why ERL is a good idea for a light sourceLetrsquos review why ERL is a good idea for a light source
Critical electron beam parameters for X-ray productionCritical electron beam parameters for X-ray production
USPAS Accelerator Physics June 2013
Introduction (contd) adiabatic damping px
p1z
p1
θ1x
electron bunch ε1
linac
px p2
p2z
θ2x
ε2 = ε1 p2z p1z
ε = εn
βγ εn is invariant since
x px = mc2βγθx form canonically conjugate variables
geometricx θx
mc2
normalized x px
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (I)
Quantum Excitation
ρ = p
eB ρ =
p eB p
eB
Equilibrium
Eph
22
~ phphE EN
dt
d
Radiative Dampingvs
Emittance (hor) Energy Spread Bunch Length
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
nfnSSc
e
dd
dEnNnn
nperp cossin
sin
22
22
22
21
2
nf
n
S
S
c
e
dd
dEnN
n
z
zn
npar
cossin
sincos1
cos
22
2
2
12
fnN is highly peaked with peak value nN around angular frequency
0 as 21
22
cos1
02
2
020
n
Kn
nn z
z
z
USPAS Accelerator Physics June 2013
Energy Distribution in Lab Frame
nfnSSc
e
dd
dEnNnn
nperp cossin
sin
22
22
22
21
2
nf
n
S
S
c
e
dd
dEnN
n
z
zn
npar
cossin
sincos1
cos
22
2
2
12
The arguments of the Bessel Functions are now
22
2
0
0
8
cos1
coscos
cos1
cossincossin
Kncdn
Kncdn
z
zzzz
zxx
(217)
USPAS Accelerator Physics June 2013
In the Forward DirectionIn the forward direction even harmonics vanish (n+2krsquo term vanishes when ldquoxrdquo Bessel function non-zero at zero argument and all other terms in sum vanish with a power higher than 2 as the argument goes to zero) and for odd harmonics only n+2krsquo=1-1 contribute to the sum
0 sin2
222
22
nf
n
KF
c
e
dd
dEnN
nnperp
0 cos2
222
22
nf
n
KF
c
e
dd
dEnN
nnpar
2
2
2
2
12
2
2
12
2
2
2
2 21421414
1
K
nKJ
K
nKJ
KnKF nn
z
n
USPAS Accelerator Physics June 2013
Number Spectral Angular Density
0 sin
22
22
nf
n
KF
dd
dNnN
nnperp
0 cos
22
22
nf
n
KF
dd
dNnN
nnpar
Converting the energy density into an number density by dividing by the photon energy (donrsquot forget both signs of frequency)
KFNdd
dNn
ntot 22
Peak value in the forward direction
USPAS Accelerator Physics June 2013
Radiation Pattern Qualitatively
Central cone high angular density region around forward direction
y
x
Central Cone
Doppler DownshiftedHarmonic Radiation
Non-zero AngularDensity Emission ata Given Frequency
r
1n
1l
2l
USPAS Accelerator Physics June 2013
Dimension Estimates
Harmonic bands at
211 2K
n
lnl
Central cone size estimated by requiring Gaussian distribution with correct peak value integrate over solid angle to the same number of total photons as integrating f
0 2
21
2
1 2
ncLnN
Kn
nr
Much narrower than typical opening angle for bend
USPAS Accelerator Physics June 2013
Number Spectral Density (Flux)
The flux in the central cone is obtained by estimating solid angle integral by the peak angular density multiplied by the Gaussian integral
Kge
IN n
nF
nKFKKg nn 21 2
2
0
n 2F rntot
d
dN
USPAS Accelerator Physics June 2013
Power Angular Density
22
22
21
cossin
sin nSSNn
d
dEnn
nperp
2
2
1
cossin
sincos1
cos
n
S
S
Nnd
dE
n
z
zn
npar
Donrsquot forget both signs of frequency
USPAS Accelerator Physics June 2013
2
2
22
222
coscos1
cos
cos14
sincos14
z
z
z
nparn
z
nperpn
KNF
d
dN
KNF
d
dN
2
2
2
2
12
2
2
122
22
21421421
K
nKJ
K
nKJ
K
KnKF nnn
For K less than or of order one
Compare with (210)
USPAS Accelerator Physics June 2013
USPAS Accelerator Physics June 2013
ERL light source ideaThird generation light sources are storage ring based facilities
optimized for production of high brilliance x-rays through spontaneous synchrotron radiation The technology is mature and while some improvement in the future is likely one ought to ask whether an alternative approach exists
Two orthogonal ideas (both linac based) are XFEL and ERL XFEL will not be spontaneous synchrotron radiation source but will deliver GW peak powers of transversely coherent radiation at very low duty factor The source parameters are very interesting and at the same time very different from any existing light source
ERL aspires to do better what storage rings are very good at to provide radiation in quasi-continuous fashion with superior brilliance monochromaticity and shorter pulses
USPAS Accelerator Physics June 2013
Coherent or incoherent
Radiation field from a single kth electron in a bunch
Radiation field from the whole bunch bunching factor (bf)
Radiation Intensity
1) ldquolong bunchrdquo =gt incoherent (conventional) SR
2) ldquoshort bunchrdquo or -bunching =gt coherent (FELs) SR
ERL hard x-ray source is envisioned to use conventional SR
)exp(0 kk tiEE
eN
kk
e
tiN
fb1
)exp(1
22
0 eNfbII
single electron
eNfb 1~2
eNII 0
1 fb 20~ eNII
USPAS Accelerator Physics June 2013
Demand for X-rays
~85 structures by ~85 structures by x-ray crystallographyx-ray crystallography
2003 Nobel Prize 2003 Nobel Prize in Chemistryin Chemistry
Roderick MacKinnonRoderick MacKinnon (Rockefeller Univ)(Rockefeller Univ)
11stst K K++ channel structure channel structure by x-ray crystallography by x-ray crystallography
based on CHESS data (1998)based on CHESS data (1998)
Ion channel proteinIon channel protein
CHESSCHESS
USPAS Accelerator Physics June 2013
X-ray characteristics neededbull for properly tuned undulator X-ray phase space is a replica from electron bunch + convolution with the diffraction limit
bull ideally one wants the phase space to be diffraction limited (ie full transverse coherence) eg rms = 4 or 01 Aring for 8 keV X-rays (Cu K) or01 m normalized at 5 GeV
Flux phs01bw
Brightness phsmrad201bw
Brilliance phsmm2mrad201bw
USPAS Accelerator Physics June 2013
Introduction
6D Phase Space Area6D Phase Space Areandash Horizontal Emittance x xrsquondash Vertical Emittance y yrsquondash Energy Spread amp Bunch length
ΔE t
Number of Electrons BunchNumber of Electrons BunchBunch Rep RateBunch Rep Rate IIpeakpeak I Iaverageaverage
Letrsquos review why ERL is a good idea for a light sourceLetrsquos review why ERL is a good idea for a light source
Critical electron beam parameters for X-ray productionCritical electron beam parameters for X-ray production
USPAS Accelerator Physics June 2013
Introduction (contd) adiabatic damping px
p1z
p1
θ1x
electron bunch ε1
linac
px p2
p2z
θ2x
ε2 = ε1 p2z p1z
ε = εn
βγ εn is invariant since
x px = mc2βγθx form canonically conjugate variables
geometricx θx
mc2
normalized x px
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (I)
Quantum Excitation
ρ = p
eB ρ =
p eB p
eB
Equilibrium
Eph
22
~ phphE EN
dt
d
Radiative Dampingvs
Emittance (hor) Energy Spread Bunch Length
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Energy Distribution in Lab Frame
nfnSSc
e
dd
dEnNnn
nperp cossin
sin
22
22
22
21
2
nf
n
S
S
c
e
dd
dEnN
n
z
zn
npar
cossin
sincos1
cos
22
2
2
12
The arguments of the Bessel Functions are now
22
2
0
0
8
cos1
coscos
cos1
cossincossin
Kncdn
Kncdn
z
zzzz
zxx
(217)
USPAS Accelerator Physics June 2013
In the Forward DirectionIn the forward direction even harmonics vanish (n+2krsquo term vanishes when ldquoxrdquo Bessel function non-zero at zero argument and all other terms in sum vanish with a power higher than 2 as the argument goes to zero) and for odd harmonics only n+2krsquo=1-1 contribute to the sum
0 sin2
222
22
nf
n
KF
c
e
dd
dEnN
nnperp
0 cos2
222
22
nf
n
KF
c
e
dd
dEnN
nnpar
2
2
2
2
12
2
2
12
2
2
2
2 21421414
1
K
nKJ
K
nKJ
KnKF nn
z
n
USPAS Accelerator Physics June 2013
Number Spectral Angular Density
0 sin
22
22
nf
n
KF
dd
dNnN
nnperp
0 cos
22
22
nf
n
KF
dd
dNnN
nnpar
Converting the energy density into an number density by dividing by the photon energy (donrsquot forget both signs of frequency)
KFNdd
dNn
ntot 22
Peak value in the forward direction
USPAS Accelerator Physics June 2013
Radiation Pattern Qualitatively
Central cone high angular density region around forward direction
y
x
Central Cone
Doppler DownshiftedHarmonic Radiation
Non-zero AngularDensity Emission ata Given Frequency
r
1n
1l
2l
USPAS Accelerator Physics June 2013
Dimension Estimates
Harmonic bands at
211 2K
n
lnl
Central cone size estimated by requiring Gaussian distribution with correct peak value integrate over solid angle to the same number of total photons as integrating f
0 2
21
2
1 2
ncLnN
Kn
nr
Much narrower than typical opening angle for bend
USPAS Accelerator Physics June 2013
Number Spectral Density (Flux)
The flux in the central cone is obtained by estimating solid angle integral by the peak angular density multiplied by the Gaussian integral
Kge
IN n
nF
nKFKKg nn 21 2
2
0
n 2F rntot
d
dN
USPAS Accelerator Physics June 2013
Power Angular Density
22
22
21
cossin
sin nSSNn
d
dEnn
nperp
2
2
1
cossin
sincos1
cos
n
S
S
Nnd
dE
n
z
zn
npar
Donrsquot forget both signs of frequency
USPAS Accelerator Physics June 2013
2
2
22
222
coscos1
cos
cos14
sincos14
z
z
z
nparn
z
nperpn
KNF
d
dN
KNF
d
dN
2
2
2
2
12
2
2
122
22
21421421
K
nKJ
K
nKJ
K
KnKF nnn
For K less than or of order one
Compare with (210)
USPAS Accelerator Physics June 2013
USPAS Accelerator Physics June 2013
ERL light source ideaThird generation light sources are storage ring based facilities
optimized for production of high brilliance x-rays through spontaneous synchrotron radiation The technology is mature and while some improvement in the future is likely one ought to ask whether an alternative approach exists
Two orthogonal ideas (both linac based) are XFEL and ERL XFEL will not be spontaneous synchrotron radiation source but will deliver GW peak powers of transversely coherent radiation at very low duty factor The source parameters are very interesting and at the same time very different from any existing light source
ERL aspires to do better what storage rings are very good at to provide radiation in quasi-continuous fashion with superior brilliance monochromaticity and shorter pulses
USPAS Accelerator Physics June 2013
Coherent or incoherent
Radiation field from a single kth electron in a bunch
Radiation field from the whole bunch bunching factor (bf)
Radiation Intensity
1) ldquolong bunchrdquo =gt incoherent (conventional) SR
2) ldquoshort bunchrdquo or -bunching =gt coherent (FELs) SR
ERL hard x-ray source is envisioned to use conventional SR
)exp(0 kk tiEE
eN
kk
e
tiN
fb1
)exp(1
22
0 eNfbII
single electron
eNfb 1~2
eNII 0
1 fb 20~ eNII
USPAS Accelerator Physics June 2013
Demand for X-rays
~85 structures by ~85 structures by x-ray crystallographyx-ray crystallography
2003 Nobel Prize 2003 Nobel Prize in Chemistryin Chemistry
Roderick MacKinnonRoderick MacKinnon (Rockefeller Univ)(Rockefeller Univ)
11stst K K++ channel structure channel structure by x-ray crystallography by x-ray crystallography
based on CHESS data (1998)based on CHESS data (1998)
Ion channel proteinIon channel protein
CHESSCHESS
USPAS Accelerator Physics June 2013
X-ray characteristics neededbull for properly tuned undulator X-ray phase space is a replica from electron bunch + convolution with the diffraction limit
bull ideally one wants the phase space to be diffraction limited (ie full transverse coherence) eg rms = 4 or 01 Aring for 8 keV X-rays (Cu K) or01 m normalized at 5 GeV
Flux phs01bw
Brightness phsmrad201bw
Brilliance phsmm2mrad201bw
USPAS Accelerator Physics June 2013
Introduction
6D Phase Space Area6D Phase Space Areandash Horizontal Emittance x xrsquondash Vertical Emittance y yrsquondash Energy Spread amp Bunch length
ΔE t
Number of Electrons BunchNumber of Electrons BunchBunch Rep RateBunch Rep Rate IIpeakpeak I Iaverageaverage
Letrsquos review why ERL is a good idea for a light sourceLetrsquos review why ERL is a good idea for a light source
Critical electron beam parameters for X-ray productionCritical electron beam parameters for X-ray production
USPAS Accelerator Physics June 2013
Introduction (contd) adiabatic damping px
p1z
p1
θ1x
electron bunch ε1
linac
px p2
p2z
θ2x
ε2 = ε1 p2z p1z
ε = εn
βγ εn is invariant since
x px = mc2βγθx form canonically conjugate variables
geometricx θx
mc2
normalized x px
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (I)
Quantum Excitation
ρ = p
eB ρ =
p eB p
eB
Equilibrium
Eph
22
~ phphE EN
dt
d
Radiative Dampingvs
Emittance (hor) Energy Spread Bunch Length
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
In the Forward DirectionIn the forward direction even harmonics vanish (n+2krsquo term vanishes when ldquoxrdquo Bessel function non-zero at zero argument and all other terms in sum vanish with a power higher than 2 as the argument goes to zero) and for odd harmonics only n+2krsquo=1-1 contribute to the sum
0 sin2
222
22
nf
n
KF
c
e
dd
dEnN
nnperp
0 cos2
222
22
nf
n
KF
c
e
dd
dEnN
nnpar
2
2
2
2
12
2
2
12
2
2
2
2 21421414
1
K
nKJ
K
nKJ
KnKF nn
z
n
USPAS Accelerator Physics June 2013
Number Spectral Angular Density
0 sin
22
22
nf
n
KF
dd
dNnN
nnperp
0 cos
22
22
nf
n
KF
dd
dNnN
nnpar
Converting the energy density into an number density by dividing by the photon energy (donrsquot forget both signs of frequency)
KFNdd
dNn
ntot 22
Peak value in the forward direction
USPAS Accelerator Physics June 2013
Radiation Pattern Qualitatively
Central cone high angular density region around forward direction
y
x
Central Cone
Doppler DownshiftedHarmonic Radiation
Non-zero AngularDensity Emission ata Given Frequency
r
1n
1l
2l
USPAS Accelerator Physics June 2013
Dimension Estimates
Harmonic bands at
211 2K
n
lnl
Central cone size estimated by requiring Gaussian distribution with correct peak value integrate over solid angle to the same number of total photons as integrating f
0 2
21
2
1 2
ncLnN
Kn
nr
Much narrower than typical opening angle for bend
USPAS Accelerator Physics June 2013
Number Spectral Density (Flux)
The flux in the central cone is obtained by estimating solid angle integral by the peak angular density multiplied by the Gaussian integral
Kge
IN n
nF
nKFKKg nn 21 2
2
0
n 2F rntot
d
dN
USPAS Accelerator Physics June 2013
Power Angular Density
22
22
21
cossin
sin nSSNn
d
dEnn
nperp
2
2
1
cossin
sincos1
cos
n
S
S
Nnd
dE
n
z
zn
npar
Donrsquot forget both signs of frequency
USPAS Accelerator Physics June 2013
2
2
22
222
coscos1
cos
cos14
sincos14
z
z
z
nparn
z
nperpn
KNF
d
dN
KNF
d
dN
2
2
2
2
12
2
2
122
22
21421421
K
nKJ
K
nKJ
K
KnKF nnn
For K less than or of order one
Compare with (210)
USPAS Accelerator Physics June 2013
USPAS Accelerator Physics June 2013
ERL light source ideaThird generation light sources are storage ring based facilities
optimized for production of high brilliance x-rays through spontaneous synchrotron radiation The technology is mature and while some improvement in the future is likely one ought to ask whether an alternative approach exists
Two orthogonal ideas (both linac based) are XFEL and ERL XFEL will not be spontaneous synchrotron radiation source but will deliver GW peak powers of transversely coherent radiation at very low duty factor The source parameters are very interesting and at the same time very different from any existing light source
ERL aspires to do better what storage rings are very good at to provide radiation in quasi-continuous fashion with superior brilliance monochromaticity and shorter pulses
USPAS Accelerator Physics June 2013
Coherent or incoherent
Radiation field from a single kth electron in a bunch
Radiation field from the whole bunch bunching factor (bf)
Radiation Intensity
1) ldquolong bunchrdquo =gt incoherent (conventional) SR
2) ldquoshort bunchrdquo or -bunching =gt coherent (FELs) SR
ERL hard x-ray source is envisioned to use conventional SR
)exp(0 kk tiEE
eN
kk
e
tiN
fb1
)exp(1
22
0 eNfbII
single electron
eNfb 1~2
eNII 0
1 fb 20~ eNII
USPAS Accelerator Physics June 2013
Demand for X-rays
~85 structures by ~85 structures by x-ray crystallographyx-ray crystallography
2003 Nobel Prize 2003 Nobel Prize in Chemistryin Chemistry
Roderick MacKinnonRoderick MacKinnon (Rockefeller Univ)(Rockefeller Univ)
11stst K K++ channel structure channel structure by x-ray crystallography by x-ray crystallography
based on CHESS data (1998)based on CHESS data (1998)
Ion channel proteinIon channel protein
CHESSCHESS
USPAS Accelerator Physics June 2013
X-ray characteristics neededbull for properly tuned undulator X-ray phase space is a replica from electron bunch + convolution with the diffraction limit
bull ideally one wants the phase space to be diffraction limited (ie full transverse coherence) eg rms = 4 or 01 Aring for 8 keV X-rays (Cu K) or01 m normalized at 5 GeV
Flux phs01bw
Brightness phsmrad201bw
Brilliance phsmm2mrad201bw
USPAS Accelerator Physics June 2013
Introduction
6D Phase Space Area6D Phase Space Areandash Horizontal Emittance x xrsquondash Vertical Emittance y yrsquondash Energy Spread amp Bunch length
ΔE t
Number of Electrons BunchNumber of Electrons BunchBunch Rep RateBunch Rep Rate IIpeakpeak I Iaverageaverage
Letrsquos review why ERL is a good idea for a light sourceLetrsquos review why ERL is a good idea for a light source
Critical electron beam parameters for X-ray productionCritical electron beam parameters for X-ray production
USPAS Accelerator Physics June 2013
Introduction (contd) adiabatic damping px
p1z
p1
θ1x
electron bunch ε1
linac
px p2
p2z
θ2x
ε2 = ε1 p2z p1z
ε = εn
βγ εn is invariant since
x px = mc2βγθx form canonically conjugate variables
geometricx θx
mc2
normalized x px
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (I)
Quantum Excitation
ρ = p
eB ρ =
p eB p
eB
Equilibrium
Eph
22
~ phphE EN
dt
d
Radiative Dampingvs
Emittance (hor) Energy Spread Bunch Length
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Number Spectral Angular Density
0 sin
22
22
nf
n
KF
dd
dNnN
nnperp
0 cos
22
22
nf
n
KF
dd
dNnN
nnpar
Converting the energy density into an number density by dividing by the photon energy (donrsquot forget both signs of frequency)
KFNdd
dNn
ntot 22
Peak value in the forward direction
USPAS Accelerator Physics June 2013
Radiation Pattern Qualitatively
Central cone high angular density region around forward direction
y
x
Central Cone
Doppler DownshiftedHarmonic Radiation
Non-zero AngularDensity Emission ata Given Frequency
r
1n
1l
2l
USPAS Accelerator Physics June 2013
Dimension Estimates
Harmonic bands at
211 2K
n
lnl
Central cone size estimated by requiring Gaussian distribution with correct peak value integrate over solid angle to the same number of total photons as integrating f
0 2
21
2
1 2
ncLnN
Kn
nr
Much narrower than typical opening angle for bend
USPAS Accelerator Physics June 2013
Number Spectral Density (Flux)
The flux in the central cone is obtained by estimating solid angle integral by the peak angular density multiplied by the Gaussian integral
Kge
IN n
nF
nKFKKg nn 21 2
2
0
n 2F rntot
d
dN
USPAS Accelerator Physics June 2013
Power Angular Density
22
22
21
cossin
sin nSSNn
d
dEnn
nperp
2
2
1
cossin
sincos1
cos
n
S
S
Nnd
dE
n
z
zn
npar
Donrsquot forget both signs of frequency
USPAS Accelerator Physics June 2013
2
2
22
222
coscos1
cos
cos14
sincos14
z
z
z
nparn
z
nperpn
KNF
d
dN
KNF
d
dN
2
2
2
2
12
2
2
122
22
21421421
K
nKJ
K
nKJ
K
KnKF nnn
For K less than or of order one
Compare with (210)
USPAS Accelerator Physics June 2013
USPAS Accelerator Physics June 2013
ERL light source ideaThird generation light sources are storage ring based facilities
optimized for production of high brilliance x-rays through spontaneous synchrotron radiation The technology is mature and while some improvement in the future is likely one ought to ask whether an alternative approach exists
Two orthogonal ideas (both linac based) are XFEL and ERL XFEL will not be spontaneous synchrotron radiation source but will deliver GW peak powers of transversely coherent radiation at very low duty factor The source parameters are very interesting and at the same time very different from any existing light source
ERL aspires to do better what storage rings are very good at to provide radiation in quasi-continuous fashion with superior brilliance monochromaticity and shorter pulses
USPAS Accelerator Physics June 2013
Coherent or incoherent
Radiation field from a single kth electron in a bunch
Radiation field from the whole bunch bunching factor (bf)
Radiation Intensity
1) ldquolong bunchrdquo =gt incoherent (conventional) SR
2) ldquoshort bunchrdquo or -bunching =gt coherent (FELs) SR
ERL hard x-ray source is envisioned to use conventional SR
)exp(0 kk tiEE
eN
kk
e
tiN
fb1
)exp(1
22
0 eNfbII
single electron
eNfb 1~2
eNII 0
1 fb 20~ eNII
USPAS Accelerator Physics June 2013
Demand for X-rays
~85 structures by ~85 structures by x-ray crystallographyx-ray crystallography
2003 Nobel Prize 2003 Nobel Prize in Chemistryin Chemistry
Roderick MacKinnonRoderick MacKinnon (Rockefeller Univ)(Rockefeller Univ)
11stst K K++ channel structure channel structure by x-ray crystallography by x-ray crystallography
based on CHESS data (1998)based on CHESS data (1998)
Ion channel proteinIon channel protein
CHESSCHESS
USPAS Accelerator Physics June 2013
X-ray characteristics neededbull for properly tuned undulator X-ray phase space is a replica from electron bunch + convolution with the diffraction limit
bull ideally one wants the phase space to be diffraction limited (ie full transverse coherence) eg rms = 4 or 01 Aring for 8 keV X-rays (Cu K) or01 m normalized at 5 GeV
Flux phs01bw
Brightness phsmrad201bw
Brilliance phsmm2mrad201bw
USPAS Accelerator Physics June 2013
Introduction
6D Phase Space Area6D Phase Space Areandash Horizontal Emittance x xrsquondash Vertical Emittance y yrsquondash Energy Spread amp Bunch length
ΔE t
Number of Electrons BunchNumber of Electrons BunchBunch Rep RateBunch Rep Rate IIpeakpeak I Iaverageaverage
Letrsquos review why ERL is a good idea for a light sourceLetrsquos review why ERL is a good idea for a light source
Critical electron beam parameters for X-ray productionCritical electron beam parameters for X-ray production
USPAS Accelerator Physics June 2013
Introduction (contd) adiabatic damping px
p1z
p1
θ1x
electron bunch ε1
linac
px p2
p2z
θ2x
ε2 = ε1 p2z p1z
ε = εn
βγ εn is invariant since
x px = mc2βγθx form canonically conjugate variables
geometricx θx
mc2
normalized x px
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (I)
Quantum Excitation
ρ = p
eB ρ =
p eB p
eB
Equilibrium
Eph
22
~ phphE EN
dt
d
Radiative Dampingvs
Emittance (hor) Energy Spread Bunch Length
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Radiation Pattern Qualitatively
Central cone high angular density region around forward direction
y
x
Central Cone
Doppler DownshiftedHarmonic Radiation
Non-zero AngularDensity Emission ata Given Frequency
r
1n
1l
2l
USPAS Accelerator Physics June 2013
Dimension Estimates
Harmonic bands at
211 2K
n
lnl
Central cone size estimated by requiring Gaussian distribution with correct peak value integrate over solid angle to the same number of total photons as integrating f
0 2
21
2
1 2
ncLnN
Kn
nr
Much narrower than typical opening angle for bend
USPAS Accelerator Physics June 2013
Number Spectral Density (Flux)
The flux in the central cone is obtained by estimating solid angle integral by the peak angular density multiplied by the Gaussian integral
Kge
IN n
nF
nKFKKg nn 21 2
2
0
n 2F rntot
d
dN
USPAS Accelerator Physics June 2013
Power Angular Density
22
22
21
cossin
sin nSSNn
d
dEnn
nperp
2
2
1
cossin
sincos1
cos
n
S
S
Nnd
dE
n
z
zn
npar
Donrsquot forget both signs of frequency
USPAS Accelerator Physics June 2013
2
2
22
222
coscos1
cos
cos14
sincos14
z
z
z
nparn
z
nperpn
KNF
d
dN
KNF
d
dN
2
2
2
2
12
2
2
122
22
21421421
K
nKJ
K
nKJ
K
KnKF nnn
For K less than or of order one
Compare with (210)
USPAS Accelerator Physics June 2013
USPAS Accelerator Physics June 2013
ERL light source ideaThird generation light sources are storage ring based facilities
optimized for production of high brilliance x-rays through spontaneous synchrotron radiation The technology is mature and while some improvement in the future is likely one ought to ask whether an alternative approach exists
Two orthogonal ideas (both linac based) are XFEL and ERL XFEL will not be spontaneous synchrotron radiation source but will deliver GW peak powers of transversely coherent radiation at very low duty factor The source parameters are very interesting and at the same time very different from any existing light source
ERL aspires to do better what storage rings are very good at to provide radiation in quasi-continuous fashion with superior brilliance monochromaticity and shorter pulses
USPAS Accelerator Physics June 2013
Coherent or incoherent
Radiation field from a single kth electron in a bunch
Radiation field from the whole bunch bunching factor (bf)
Radiation Intensity
1) ldquolong bunchrdquo =gt incoherent (conventional) SR
2) ldquoshort bunchrdquo or -bunching =gt coherent (FELs) SR
ERL hard x-ray source is envisioned to use conventional SR
)exp(0 kk tiEE
eN
kk
e
tiN
fb1
)exp(1
22
0 eNfbII
single electron
eNfb 1~2
eNII 0
1 fb 20~ eNII
USPAS Accelerator Physics June 2013
Demand for X-rays
~85 structures by ~85 structures by x-ray crystallographyx-ray crystallography
2003 Nobel Prize 2003 Nobel Prize in Chemistryin Chemistry
Roderick MacKinnonRoderick MacKinnon (Rockefeller Univ)(Rockefeller Univ)
11stst K K++ channel structure channel structure by x-ray crystallography by x-ray crystallography
based on CHESS data (1998)based on CHESS data (1998)
Ion channel proteinIon channel protein
CHESSCHESS
USPAS Accelerator Physics June 2013
X-ray characteristics neededbull for properly tuned undulator X-ray phase space is a replica from electron bunch + convolution with the diffraction limit
bull ideally one wants the phase space to be diffraction limited (ie full transverse coherence) eg rms = 4 or 01 Aring for 8 keV X-rays (Cu K) or01 m normalized at 5 GeV
Flux phs01bw
Brightness phsmrad201bw
Brilliance phsmm2mrad201bw
USPAS Accelerator Physics June 2013
Introduction
6D Phase Space Area6D Phase Space Areandash Horizontal Emittance x xrsquondash Vertical Emittance y yrsquondash Energy Spread amp Bunch length
ΔE t
Number of Electrons BunchNumber of Electrons BunchBunch Rep RateBunch Rep Rate IIpeakpeak I Iaverageaverage
Letrsquos review why ERL is a good idea for a light sourceLetrsquos review why ERL is a good idea for a light source
Critical electron beam parameters for X-ray productionCritical electron beam parameters for X-ray production
USPAS Accelerator Physics June 2013
Introduction (contd) adiabatic damping px
p1z
p1
θ1x
electron bunch ε1
linac
px p2
p2z
θ2x
ε2 = ε1 p2z p1z
ε = εn
βγ εn is invariant since
x px = mc2βγθx form canonically conjugate variables
geometricx θx
mc2
normalized x px
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (I)
Quantum Excitation
ρ = p
eB ρ =
p eB p
eB
Equilibrium
Eph
22
~ phphE EN
dt
d
Radiative Dampingvs
Emittance (hor) Energy Spread Bunch Length
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Dimension Estimates
Harmonic bands at
211 2K
n
lnl
Central cone size estimated by requiring Gaussian distribution with correct peak value integrate over solid angle to the same number of total photons as integrating f
0 2
21
2
1 2
ncLnN
Kn
nr
Much narrower than typical opening angle for bend
USPAS Accelerator Physics June 2013
Number Spectral Density (Flux)
The flux in the central cone is obtained by estimating solid angle integral by the peak angular density multiplied by the Gaussian integral
Kge
IN n
nF
nKFKKg nn 21 2
2
0
n 2F rntot
d
dN
USPAS Accelerator Physics June 2013
Power Angular Density
22
22
21
cossin
sin nSSNn
d
dEnn
nperp
2
2
1
cossin
sincos1
cos
n
S
S
Nnd
dE
n
z
zn
npar
Donrsquot forget both signs of frequency
USPAS Accelerator Physics June 2013
2
2
22
222
coscos1
cos
cos14
sincos14
z
z
z
nparn
z
nperpn
KNF
d
dN
KNF
d
dN
2
2
2
2
12
2
2
122
22
21421421
K
nKJ
K
nKJ
K
KnKF nnn
For K less than or of order one
Compare with (210)
USPAS Accelerator Physics June 2013
USPAS Accelerator Physics June 2013
ERL light source ideaThird generation light sources are storage ring based facilities
optimized for production of high brilliance x-rays through spontaneous synchrotron radiation The technology is mature and while some improvement in the future is likely one ought to ask whether an alternative approach exists
Two orthogonal ideas (both linac based) are XFEL and ERL XFEL will not be spontaneous synchrotron radiation source but will deliver GW peak powers of transversely coherent radiation at very low duty factor The source parameters are very interesting and at the same time very different from any existing light source
ERL aspires to do better what storage rings are very good at to provide radiation in quasi-continuous fashion with superior brilliance monochromaticity and shorter pulses
USPAS Accelerator Physics June 2013
Coherent or incoherent
Radiation field from a single kth electron in a bunch
Radiation field from the whole bunch bunching factor (bf)
Radiation Intensity
1) ldquolong bunchrdquo =gt incoherent (conventional) SR
2) ldquoshort bunchrdquo or -bunching =gt coherent (FELs) SR
ERL hard x-ray source is envisioned to use conventional SR
)exp(0 kk tiEE
eN
kk
e
tiN
fb1
)exp(1
22
0 eNfbII
single electron
eNfb 1~2
eNII 0
1 fb 20~ eNII
USPAS Accelerator Physics June 2013
Demand for X-rays
~85 structures by ~85 structures by x-ray crystallographyx-ray crystallography
2003 Nobel Prize 2003 Nobel Prize in Chemistryin Chemistry
Roderick MacKinnonRoderick MacKinnon (Rockefeller Univ)(Rockefeller Univ)
11stst K K++ channel structure channel structure by x-ray crystallography by x-ray crystallography
based on CHESS data (1998)based on CHESS data (1998)
Ion channel proteinIon channel protein
CHESSCHESS
USPAS Accelerator Physics June 2013
X-ray characteristics neededbull for properly tuned undulator X-ray phase space is a replica from electron bunch + convolution with the diffraction limit
bull ideally one wants the phase space to be diffraction limited (ie full transverse coherence) eg rms = 4 or 01 Aring for 8 keV X-rays (Cu K) or01 m normalized at 5 GeV
Flux phs01bw
Brightness phsmrad201bw
Brilliance phsmm2mrad201bw
USPAS Accelerator Physics June 2013
Introduction
6D Phase Space Area6D Phase Space Areandash Horizontal Emittance x xrsquondash Vertical Emittance y yrsquondash Energy Spread amp Bunch length
ΔE t
Number of Electrons BunchNumber of Electrons BunchBunch Rep RateBunch Rep Rate IIpeakpeak I Iaverageaverage
Letrsquos review why ERL is a good idea for a light sourceLetrsquos review why ERL is a good idea for a light source
Critical electron beam parameters for X-ray productionCritical electron beam parameters for X-ray production
USPAS Accelerator Physics June 2013
Introduction (contd) adiabatic damping px
p1z
p1
θ1x
electron bunch ε1
linac
px p2
p2z
θ2x
ε2 = ε1 p2z p1z
ε = εn
βγ εn is invariant since
x px = mc2βγθx form canonically conjugate variables
geometricx θx
mc2
normalized x px
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (I)
Quantum Excitation
ρ = p
eB ρ =
p eB p
eB
Equilibrium
Eph
22
~ phphE EN
dt
d
Radiative Dampingvs
Emittance (hor) Energy Spread Bunch Length
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Number Spectral Density (Flux)
The flux in the central cone is obtained by estimating solid angle integral by the peak angular density multiplied by the Gaussian integral
Kge
IN n
nF
nKFKKg nn 21 2
2
0
n 2F rntot
d
dN
USPAS Accelerator Physics June 2013
Power Angular Density
22
22
21
cossin
sin nSSNn
d
dEnn
nperp
2
2
1
cossin
sincos1
cos
n
S
S
Nnd
dE
n
z
zn
npar
Donrsquot forget both signs of frequency
USPAS Accelerator Physics June 2013
2
2
22
222
coscos1
cos
cos14
sincos14
z
z
z
nparn
z
nperpn
KNF
d
dN
KNF
d
dN
2
2
2
2
12
2
2
122
22
21421421
K
nKJ
K
nKJ
K
KnKF nnn
For K less than or of order one
Compare with (210)
USPAS Accelerator Physics June 2013
USPAS Accelerator Physics June 2013
ERL light source ideaThird generation light sources are storage ring based facilities
optimized for production of high brilliance x-rays through spontaneous synchrotron radiation The technology is mature and while some improvement in the future is likely one ought to ask whether an alternative approach exists
Two orthogonal ideas (both linac based) are XFEL and ERL XFEL will not be spontaneous synchrotron radiation source but will deliver GW peak powers of transversely coherent radiation at very low duty factor The source parameters are very interesting and at the same time very different from any existing light source
ERL aspires to do better what storage rings are very good at to provide radiation in quasi-continuous fashion with superior brilliance monochromaticity and shorter pulses
USPAS Accelerator Physics June 2013
Coherent or incoherent
Radiation field from a single kth electron in a bunch
Radiation field from the whole bunch bunching factor (bf)
Radiation Intensity
1) ldquolong bunchrdquo =gt incoherent (conventional) SR
2) ldquoshort bunchrdquo or -bunching =gt coherent (FELs) SR
ERL hard x-ray source is envisioned to use conventional SR
)exp(0 kk tiEE
eN
kk
e
tiN
fb1
)exp(1
22
0 eNfbII
single electron
eNfb 1~2
eNII 0
1 fb 20~ eNII
USPAS Accelerator Physics June 2013
Demand for X-rays
~85 structures by ~85 structures by x-ray crystallographyx-ray crystallography
2003 Nobel Prize 2003 Nobel Prize in Chemistryin Chemistry
Roderick MacKinnonRoderick MacKinnon (Rockefeller Univ)(Rockefeller Univ)
11stst K K++ channel structure channel structure by x-ray crystallography by x-ray crystallography
based on CHESS data (1998)based on CHESS data (1998)
Ion channel proteinIon channel protein
CHESSCHESS
USPAS Accelerator Physics June 2013
X-ray characteristics neededbull for properly tuned undulator X-ray phase space is a replica from electron bunch + convolution with the diffraction limit
bull ideally one wants the phase space to be diffraction limited (ie full transverse coherence) eg rms = 4 or 01 Aring for 8 keV X-rays (Cu K) or01 m normalized at 5 GeV
Flux phs01bw
Brightness phsmrad201bw
Brilliance phsmm2mrad201bw
USPAS Accelerator Physics June 2013
Introduction
6D Phase Space Area6D Phase Space Areandash Horizontal Emittance x xrsquondash Vertical Emittance y yrsquondash Energy Spread amp Bunch length
ΔE t
Number of Electrons BunchNumber of Electrons BunchBunch Rep RateBunch Rep Rate IIpeakpeak I Iaverageaverage
Letrsquos review why ERL is a good idea for a light sourceLetrsquos review why ERL is a good idea for a light source
Critical electron beam parameters for X-ray productionCritical electron beam parameters for X-ray production
USPAS Accelerator Physics June 2013
Introduction (contd) adiabatic damping px
p1z
p1
θ1x
electron bunch ε1
linac
px p2
p2z
θ2x
ε2 = ε1 p2z p1z
ε = εn
βγ εn is invariant since
x px = mc2βγθx form canonically conjugate variables
geometricx θx
mc2
normalized x px
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (I)
Quantum Excitation
ρ = p
eB ρ =
p eB p
eB
Equilibrium
Eph
22
~ phphE EN
dt
d
Radiative Dampingvs
Emittance (hor) Energy Spread Bunch Length
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Power Angular Density
22
22
21
cossin
sin nSSNn
d
dEnn
nperp
2
2
1
cossin
sincos1
cos
n
S
S
Nnd
dE
n
z
zn
npar
Donrsquot forget both signs of frequency
USPAS Accelerator Physics June 2013
2
2
22
222
coscos1
cos
cos14
sincos14
z
z
z
nparn
z
nperpn
KNF
d
dN
KNF
d
dN
2
2
2
2
12
2
2
122
22
21421421
K
nKJ
K
nKJ
K
KnKF nnn
For K less than or of order one
Compare with (210)
USPAS Accelerator Physics June 2013
USPAS Accelerator Physics June 2013
ERL light source ideaThird generation light sources are storage ring based facilities
optimized for production of high brilliance x-rays through spontaneous synchrotron radiation The technology is mature and while some improvement in the future is likely one ought to ask whether an alternative approach exists
Two orthogonal ideas (both linac based) are XFEL and ERL XFEL will not be spontaneous synchrotron radiation source but will deliver GW peak powers of transversely coherent radiation at very low duty factor The source parameters are very interesting and at the same time very different from any existing light source
ERL aspires to do better what storage rings are very good at to provide radiation in quasi-continuous fashion with superior brilliance monochromaticity and shorter pulses
USPAS Accelerator Physics June 2013
Coherent or incoherent
Radiation field from a single kth electron in a bunch
Radiation field from the whole bunch bunching factor (bf)
Radiation Intensity
1) ldquolong bunchrdquo =gt incoherent (conventional) SR
2) ldquoshort bunchrdquo or -bunching =gt coherent (FELs) SR
ERL hard x-ray source is envisioned to use conventional SR
)exp(0 kk tiEE
eN
kk
e
tiN
fb1
)exp(1
22
0 eNfbII
single electron
eNfb 1~2
eNII 0
1 fb 20~ eNII
USPAS Accelerator Physics June 2013
Demand for X-rays
~85 structures by ~85 structures by x-ray crystallographyx-ray crystallography
2003 Nobel Prize 2003 Nobel Prize in Chemistryin Chemistry
Roderick MacKinnonRoderick MacKinnon (Rockefeller Univ)(Rockefeller Univ)
11stst K K++ channel structure channel structure by x-ray crystallography by x-ray crystallography
based on CHESS data (1998)based on CHESS data (1998)
Ion channel proteinIon channel protein
CHESSCHESS
USPAS Accelerator Physics June 2013
X-ray characteristics neededbull for properly tuned undulator X-ray phase space is a replica from electron bunch + convolution with the diffraction limit
bull ideally one wants the phase space to be diffraction limited (ie full transverse coherence) eg rms = 4 or 01 Aring for 8 keV X-rays (Cu K) or01 m normalized at 5 GeV
Flux phs01bw
Brightness phsmrad201bw
Brilliance phsmm2mrad201bw
USPAS Accelerator Physics June 2013
Introduction
6D Phase Space Area6D Phase Space Areandash Horizontal Emittance x xrsquondash Vertical Emittance y yrsquondash Energy Spread amp Bunch length
ΔE t
Number of Electrons BunchNumber of Electrons BunchBunch Rep RateBunch Rep Rate IIpeakpeak I Iaverageaverage
Letrsquos review why ERL is a good idea for a light sourceLetrsquos review why ERL is a good idea for a light source
Critical electron beam parameters for X-ray productionCritical electron beam parameters for X-ray production
USPAS Accelerator Physics June 2013
Introduction (contd) adiabatic damping px
p1z
p1
θ1x
electron bunch ε1
linac
px p2
p2z
θ2x
ε2 = ε1 p2z p1z
ε = εn
βγ εn is invariant since
x px = mc2βγθx form canonically conjugate variables
geometricx θx
mc2
normalized x px
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (I)
Quantum Excitation
ρ = p
eB ρ =
p eB p
eB
Equilibrium
Eph
22
~ phphE EN
dt
d
Radiative Dampingvs
Emittance (hor) Energy Spread Bunch Length
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
2
2
22
222
coscos1
cos
cos14
sincos14
z
z
z
nparn
z
nperpn
KNF
d
dN
KNF
d
dN
2
2
2
2
12
2
2
122
22
21421421
K
nKJ
K
nKJ
K
KnKF nnn
For K less than or of order one
Compare with (210)
USPAS Accelerator Physics June 2013
USPAS Accelerator Physics June 2013
ERL light source ideaThird generation light sources are storage ring based facilities
optimized for production of high brilliance x-rays through spontaneous synchrotron radiation The technology is mature and while some improvement in the future is likely one ought to ask whether an alternative approach exists
Two orthogonal ideas (both linac based) are XFEL and ERL XFEL will not be spontaneous synchrotron radiation source but will deliver GW peak powers of transversely coherent radiation at very low duty factor The source parameters are very interesting and at the same time very different from any existing light source
ERL aspires to do better what storage rings are very good at to provide radiation in quasi-continuous fashion with superior brilliance monochromaticity and shorter pulses
USPAS Accelerator Physics June 2013
Coherent or incoherent
Radiation field from a single kth electron in a bunch
Radiation field from the whole bunch bunching factor (bf)
Radiation Intensity
1) ldquolong bunchrdquo =gt incoherent (conventional) SR
2) ldquoshort bunchrdquo or -bunching =gt coherent (FELs) SR
ERL hard x-ray source is envisioned to use conventional SR
)exp(0 kk tiEE
eN
kk
e
tiN
fb1
)exp(1
22
0 eNfbII
single electron
eNfb 1~2
eNII 0
1 fb 20~ eNII
USPAS Accelerator Physics June 2013
Demand for X-rays
~85 structures by ~85 structures by x-ray crystallographyx-ray crystallography
2003 Nobel Prize 2003 Nobel Prize in Chemistryin Chemistry
Roderick MacKinnonRoderick MacKinnon (Rockefeller Univ)(Rockefeller Univ)
11stst K K++ channel structure channel structure by x-ray crystallography by x-ray crystallography
based on CHESS data (1998)based on CHESS data (1998)
Ion channel proteinIon channel protein
CHESSCHESS
USPAS Accelerator Physics June 2013
X-ray characteristics neededbull for properly tuned undulator X-ray phase space is a replica from electron bunch + convolution with the diffraction limit
bull ideally one wants the phase space to be diffraction limited (ie full transverse coherence) eg rms = 4 or 01 Aring for 8 keV X-rays (Cu K) or01 m normalized at 5 GeV
Flux phs01bw
Brightness phsmrad201bw
Brilliance phsmm2mrad201bw
USPAS Accelerator Physics June 2013
Introduction
6D Phase Space Area6D Phase Space Areandash Horizontal Emittance x xrsquondash Vertical Emittance y yrsquondash Energy Spread amp Bunch length
ΔE t
Number of Electrons BunchNumber of Electrons BunchBunch Rep RateBunch Rep Rate IIpeakpeak I Iaverageaverage
Letrsquos review why ERL is a good idea for a light sourceLetrsquos review why ERL is a good idea for a light source
Critical electron beam parameters for X-ray productionCritical electron beam parameters for X-ray production
USPAS Accelerator Physics June 2013
Introduction (contd) adiabatic damping px
p1z
p1
θ1x
electron bunch ε1
linac
px p2
p2z
θ2x
ε2 = ε1 p2z p1z
ε = εn
βγ εn is invariant since
x px = mc2βγθx form canonically conjugate variables
geometricx θx
mc2
normalized x px
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (I)
Quantum Excitation
ρ = p
eB ρ =
p eB p
eB
Equilibrium
Eph
22
~ phphE EN
dt
d
Radiative Dampingvs
Emittance (hor) Energy Spread Bunch Length
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
USPAS Accelerator Physics June 2013
ERL light source ideaThird generation light sources are storage ring based facilities
optimized for production of high brilliance x-rays through spontaneous synchrotron radiation The technology is mature and while some improvement in the future is likely one ought to ask whether an alternative approach exists
Two orthogonal ideas (both linac based) are XFEL and ERL XFEL will not be spontaneous synchrotron radiation source but will deliver GW peak powers of transversely coherent radiation at very low duty factor The source parameters are very interesting and at the same time very different from any existing light source
ERL aspires to do better what storage rings are very good at to provide radiation in quasi-continuous fashion with superior brilliance monochromaticity and shorter pulses
USPAS Accelerator Physics June 2013
Coherent or incoherent
Radiation field from a single kth electron in a bunch
Radiation field from the whole bunch bunching factor (bf)
Radiation Intensity
1) ldquolong bunchrdquo =gt incoherent (conventional) SR
2) ldquoshort bunchrdquo or -bunching =gt coherent (FELs) SR
ERL hard x-ray source is envisioned to use conventional SR
)exp(0 kk tiEE
eN
kk
e
tiN
fb1
)exp(1
22
0 eNfbII
single electron
eNfb 1~2
eNII 0
1 fb 20~ eNII
USPAS Accelerator Physics June 2013
Demand for X-rays
~85 structures by ~85 structures by x-ray crystallographyx-ray crystallography
2003 Nobel Prize 2003 Nobel Prize in Chemistryin Chemistry
Roderick MacKinnonRoderick MacKinnon (Rockefeller Univ)(Rockefeller Univ)
11stst K K++ channel structure channel structure by x-ray crystallography by x-ray crystallography
based on CHESS data (1998)based on CHESS data (1998)
Ion channel proteinIon channel protein
CHESSCHESS
USPAS Accelerator Physics June 2013
X-ray characteristics neededbull for properly tuned undulator X-ray phase space is a replica from electron bunch + convolution with the diffraction limit
bull ideally one wants the phase space to be diffraction limited (ie full transverse coherence) eg rms = 4 or 01 Aring for 8 keV X-rays (Cu K) or01 m normalized at 5 GeV
Flux phs01bw
Brightness phsmrad201bw
Brilliance phsmm2mrad201bw
USPAS Accelerator Physics June 2013
Introduction
6D Phase Space Area6D Phase Space Areandash Horizontal Emittance x xrsquondash Vertical Emittance y yrsquondash Energy Spread amp Bunch length
ΔE t
Number of Electrons BunchNumber of Electrons BunchBunch Rep RateBunch Rep Rate IIpeakpeak I Iaverageaverage
Letrsquos review why ERL is a good idea for a light sourceLetrsquos review why ERL is a good idea for a light source
Critical electron beam parameters for X-ray productionCritical electron beam parameters for X-ray production
USPAS Accelerator Physics June 2013
Introduction (contd) adiabatic damping px
p1z
p1
θ1x
electron bunch ε1
linac
px p2
p2z
θ2x
ε2 = ε1 p2z p1z
ε = εn
βγ εn is invariant since
x px = mc2βγθx form canonically conjugate variables
geometricx θx
mc2
normalized x px
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (I)
Quantum Excitation
ρ = p
eB ρ =
p eB p
eB
Equilibrium
Eph
22
~ phphE EN
dt
d
Radiative Dampingvs
Emittance (hor) Energy Spread Bunch Length
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
ERL light source ideaThird generation light sources are storage ring based facilities
optimized for production of high brilliance x-rays through spontaneous synchrotron radiation The technology is mature and while some improvement in the future is likely one ought to ask whether an alternative approach exists
Two orthogonal ideas (both linac based) are XFEL and ERL XFEL will not be spontaneous synchrotron radiation source but will deliver GW peak powers of transversely coherent radiation at very low duty factor The source parameters are very interesting and at the same time very different from any existing light source
ERL aspires to do better what storage rings are very good at to provide radiation in quasi-continuous fashion with superior brilliance monochromaticity and shorter pulses
USPAS Accelerator Physics June 2013
Coherent or incoherent
Radiation field from a single kth electron in a bunch
Radiation field from the whole bunch bunching factor (bf)
Radiation Intensity
1) ldquolong bunchrdquo =gt incoherent (conventional) SR
2) ldquoshort bunchrdquo or -bunching =gt coherent (FELs) SR
ERL hard x-ray source is envisioned to use conventional SR
)exp(0 kk tiEE
eN
kk
e
tiN
fb1
)exp(1
22
0 eNfbII
single electron
eNfb 1~2
eNII 0
1 fb 20~ eNII
USPAS Accelerator Physics June 2013
Demand for X-rays
~85 structures by ~85 structures by x-ray crystallographyx-ray crystallography
2003 Nobel Prize 2003 Nobel Prize in Chemistryin Chemistry
Roderick MacKinnonRoderick MacKinnon (Rockefeller Univ)(Rockefeller Univ)
11stst K K++ channel structure channel structure by x-ray crystallography by x-ray crystallography
based on CHESS data (1998)based on CHESS data (1998)
Ion channel proteinIon channel protein
CHESSCHESS
USPAS Accelerator Physics June 2013
X-ray characteristics neededbull for properly tuned undulator X-ray phase space is a replica from electron bunch + convolution with the diffraction limit
bull ideally one wants the phase space to be diffraction limited (ie full transverse coherence) eg rms = 4 or 01 Aring for 8 keV X-rays (Cu K) or01 m normalized at 5 GeV
Flux phs01bw
Brightness phsmrad201bw
Brilliance phsmm2mrad201bw
USPAS Accelerator Physics June 2013
Introduction
6D Phase Space Area6D Phase Space Areandash Horizontal Emittance x xrsquondash Vertical Emittance y yrsquondash Energy Spread amp Bunch length
ΔE t
Number of Electrons BunchNumber of Electrons BunchBunch Rep RateBunch Rep Rate IIpeakpeak I Iaverageaverage
Letrsquos review why ERL is a good idea for a light sourceLetrsquos review why ERL is a good idea for a light source
Critical electron beam parameters for X-ray productionCritical electron beam parameters for X-ray production
USPAS Accelerator Physics June 2013
Introduction (contd) adiabatic damping px
p1z
p1
θ1x
electron bunch ε1
linac
px p2
p2z
θ2x
ε2 = ε1 p2z p1z
ε = εn
βγ εn is invariant since
x px = mc2βγθx form canonically conjugate variables
geometricx θx
mc2
normalized x px
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (I)
Quantum Excitation
ρ = p
eB ρ =
p eB p
eB
Equilibrium
Eph
22
~ phphE EN
dt
d
Radiative Dampingvs
Emittance (hor) Energy Spread Bunch Length
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Coherent or incoherent
Radiation field from a single kth electron in a bunch
Radiation field from the whole bunch bunching factor (bf)
Radiation Intensity
1) ldquolong bunchrdquo =gt incoherent (conventional) SR
2) ldquoshort bunchrdquo or -bunching =gt coherent (FELs) SR
ERL hard x-ray source is envisioned to use conventional SR
)exp(0 kk tiEE
eN
kk
e
tiN
fb1
)exp(1
22
0 eNfbII
single electron
eNfb 1~2
eNII 0
1 fb 20~ eNII
USPAS Accelerator Physics June 2013
Demand for X-rays
~85 structures by ~85 structures by x-ray crystallographyx-ray crystallography
2003 Nobel Prize 2003 Nobel Prize in Chemistryin Chemistry
Roderick MacKinnonRoderick MacKinnon (Rockefeller Univ)(Rockefeller Univ)
11stst K K++ channel structure channel structure by x-ray crystallography by x-ray crystallography
based on CHESS data (1998)based on CHESS data (1998)
Ion channel proteinIon channel protein
CHESSCHESS
USPAS Accelerator Physics June 2013
X-ray characteristics neededbull for properly tuned undulator X-ray phase space is a replica from electron bunch + convolution with the diffraction limit
bull ideally one wants the phase space to be diffraction limited (ie full transverse coherence) eg rms = 4 or 01 Aring for 8 keV X-rays (Cu K) or01 m normalized at 5 GeV
Flux phs01bw
Brightness phsmrad201bw
Brilliance phsmm2mrad201bw
USPAS Accelerator Physics June 2013
Introduction
6D Phase Space Area6D Phase Space Areandash Horizontal Emittance x xrsquondash Vertical Emittance y yrsquondash Energy Spread amp Bunch length
ΔE t
Number of Electrons BunchNumber of Electrons BunchBunch Rep RateBunch Rep Rate IIpeakpeak I Iaverageaverage
Letrsquos review why ERL is a good idea for a light sourceLetrsquos review why ERL is a good idea for a light source
Critical electron beam parameters for X-ray productionCritical electron beam parameters for X-ray production
USPAS Accelerator Physics June 2013
Introduction (contd) adiabatic damping px
p1z
p1
θ1x
electron bunch ε1
linac
px p2
p2z
θ2x
ε2 = ε1 p2z p1z
ε = εn
βγ εn is invariant since
x px = mc2βγθx form canonically conjugate variables
geometricx θx
mc2
normalized x px
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (I)
Quantum Excitation
ρ = p
eB ρ =
p eB p
eB
Equilibrium
Eph
22
~ phphE EN
dt
d
Radiative Dampingvs
Emittance (hor) Energy Spread Bunch Length
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Demand for X-rays
~85 structures by ~85 structures by x-ray crystallographyx-ray crystallography
2003 Nobel Prize 2003 Nobel Prize in Chemistryin Chemistry
Roderick MacKinnonRoderick MacKinnon (Rockefeller Univ)(Rockefeller Univ)
11stst K K++ channel structure channel structure by x-ray crystallography by x-ray crystallography
based on CHESS data (1998)based on CHESS data (1998)
Ion channel proteinIon channel protein
CHESSCHESS
USPAS Accelerator Physics June 2013
X-ray characteristics neededbull for properly tuned undulator X-ray phase space is a replica from electron bunch + convolution with the diffraction limit
bull ideally one wants the phase space to be diffraction limited (ie full transverse coherence) eg rms = 4 or 01 Aring for 8 keV X-rays (Cu K) or01 m normalized at 5 GeV
Flux phs01bw
Brightness phsmrad201bw
Brilliance phsmm2mrad201bw
USPAS Accelerator Physics June 2013
Introduction
6D Phase Space Area6D Phase Space Areandash Horizontal Emittance x xrsquondash Vertical Emittance y yrsquondash Energy Spread amp Bunch length
ΔE t
Number of Electrons BunchNumber of Electrons BunchBunch Rep RateBunch Rep Rate IIpeakpeak I Iaverageaverage
Letrsquos review why ERL is a good idea for a light sourceLetrsquos review why ERL is a good idea for a light source
Critical electron beam parameters for X-ray productionCritical electron beam parameters for X-ray production
USPAS Accelerator Physics June 2013
Introduction (contd) adiabatic damping px
p1z
p1
θ1x
electron bunch ε1
linac
px p2
p2z
θ2x
ε2 = ε1 p2z p1z
ε = εn
βγ εn is invariant since
x px = mc2βγθx form canonically conjugate variables
geometricx θx
mc2
normalized x px
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (I)
Quantum Excitation
ρ = p
eB ρ =
p eB p
eB
Equilibrium
Eph
22
~ phphE EN
dt
d
Radiative Dampingvs
Emittance (hor) Energy Spread Bunch Length
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
X-ray characteristics neededbull for properly tuned undulator X-ray phase space is a replica from electron bunch + convolution with the diffraction limit
bull ideally one wants the phase space to be diffraction limited (ie full transverse coherence) eg rms = 4 or 01 Aring for 8 keV X-rays (Cu K) or01 m normalized at 5 GeV
Flux phs01bw
Brightness phsmrad201bw
Brilliance phsmm2mrad201bw
USPAS Accelerator Physics June 2013
Introduction
6D Phase Space Area6D Phase Space Areandash Horizontal Emittance x xrsquondash Vertical Emittance y yrsquondash Energy Spread amp Bunch length
ΔE t
Number of Electrons BunchNumber of Electrons BunchBunch Rep RateBunch Rep Rate IIpeakpeak I Iaverageaverage
Letrsquos review why ERL is a good idea for a light sourceLetrsquos review why ERL is a good idea for a light source
Critical electron beam parameters for X-ray productionCritical electron beam parameters for X-ray production
USPAS Accelerator Physics June 2013
Introduction (contd) adiabatic damping px
p1z
p1
θ1x
electron bunch ε1
linac
px p2
p2z
θ2x
ε2 = ε1 p2z p1z
ε = εn
βγ εn is invariant since
x px = mc2βγθx form canonically conjugate variables
geometricx θx
mc2
normalized x px
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (I)
Quantum Excitation
ρ = p
eB ρ =
p eB p
eB
Equilibrium
Eph
22
~ phphE EN
dt
d
Radiative Dampingvs
Emittance (hor) Energy Spread Bunch Length
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Introduction
6D Phase Space Area6D Phase Space Areandash Horizontal Emittance x xrsquondash Vertical Emittance y yrsquondash Energy Spread amp Bunch length
ΔE t
Number of Electrons BunchNumber of Electrons BunchBunch Rep RateBunch Rep Rate IIpeakpeak I Iaverageaverage
Letrsquos review why ERL is a good idea for a light sourceLetrsquos review why ERL is a good idea for a light source
Critical electron beam parameters for X-ray productionCritical electron beam parameters for X-ray production
USPAS Accelerator Physics June 2013
Introduction (contd) adiabatic damping px
p1z
p1
θ1x
electron bunch ε1
linac
px p2
p2z
θ2x
ε2 = ε1 p2z p1z
ε = εn
βγ εn is invariant since
x px = mc2βγθx form canonically conjugate variables
geometricx θx
mc2
normalized x px
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (I)
Quantum Excitation
ρ = p
eB ρ =
p eB p
eB
Equilibrium
Eph
22
~ phphE EN
dt
d
Radiative Dampingvs
Emittance (hor) Energy Spread Bunch Length
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Introduction (contd) adiabatic damping px
p1z
p1
θ1x
electron bunch ε1
linac
px p2
p2z
θ2x
ε2 = ε1 p2z p1z
ε = εn
βγ εn is invariant since
x px = mc2βγθx form canonically conjugate variables
geometricx θx
mc2
normalized x px
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (I)
Quantum Excitation
ρ = p
eB ρ =
p eB p
eB
Equilibrium
Eph
22
~ phphE EN
dt
d
Radiative Dampingvs
Emittance (hor) Energy Spread Bunch Length
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Introduction (contd) storage rings (I)
Quantum Excitation
ρ = p
eB ρ =
p eB p
eB
Equilibrium
Eph
22
~ phphE EN
dt
d
Radiative Dampingvs
Emittance (hor) Energy Spread Bunch Length
USPAS Accelerator Physics June 2013
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Introduction (contd) storage rings (II)
Touschek Effect
Beam Lifetime vs Space Charge Density
bull
bull e 1
e 2
x
z
p 1 in
p 2 in
p 1 out p 2 out
USPAS Accelerator Physics June 2013
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Introduction (contd) why ERL
ESRF 6 GeV 200 mAεx = 4 nm mradεy = 002 nm mradB ~ 1020 phsmm2mrad201BWLID = 5 m
ERL 5 GeV 10-100 mAεx = εy 001 nm mradB ~ 1023 phsmm2mrad201BWLID = 25 m
ESRFERL (no compression)
ERL (w compression)
t
USPAS Accelerator Physics June 2013
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Comparing present and future sources
A(nm-rad)2 max Nund
electron beam brilliance electron beam monochromaticity2222 )4()4( yxI )(51 EE
A(nm-rad)2 compares brilliance from two short identical (K Nund) undulators
A(nm-rad)2 max Nund compares maximum achievable brilliance
USPAS Accelerator Physics June 2013
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
1 Angstrom brilliance comparison
ERL better by
ERL emittance is taken to be (PRSTAB 8 (2005) 034202)n[mm-mrad] (073+015z[mm]23) q[nC]
plus a factor of 2 emittance growth for horizontal
USPAS Accelerator Physics June 2013
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Cornell vision of ERL light sourceTo continue the long-standing tradition of pioneering research in
synchrotron radiation Cornell University is carefully looking into constructing a first ERL hard x-ray light source
But firsthellip
SASE
USPAS Accelerator Physics June 2013
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Need for the ERL prototypeIssues include
CW injector produce iavg 100 mA qbunch ~ 80 pC 1300 MHz n lt 1 mm mr low halo with very good photo-cathode longevity
Maintain high Q and Eacc in high current beam conditions
Extract HOMrsquos with very high efficiency (PHOM ~ 10x
previous )
Control BBU by improved HOM damping parameterize ithr
How to operate with hi QL (control microphonics amp Lorentz detuning)
Produce + meas t ~ 100 fs with qbunch ~ 03ndash04 nC (iavg 100 mA) understand control CSR understand limits on simultaneous brilliance and short pulses
Check improve beam codes Investigate multipass schemes
Our conclusion An ERL Prototype is needed to resolve outstandingOur conclusion An ERL Prototype is needed to resolve outstandingtechnology and accelerator physics issues before a large ERL is builttechnology and accelerator physics issues before a large ERL is built
USPAS Accelerator Physics June 2013
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Cornell ERL Prototype
Energy 100 MeVMax Avg Current 100 mACharge bunch 1 ndash 400 pCEmittance (norm) 2 mm mr77 pC
Injection Energy 5 ndash 15 MeVEacc Q0 20 MeVm 1010
Bunch Length 2 ndash 01 ps
USPAS Accelerator Physics June 2013
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Cornell ERL Phase I Injector
Beam Energy Range 5 ndash 15a MeVMax Average Beam Current 100 mAMax Bunch Rep Rate 77 pC 13 GHzTransverse Emittance rms (norm) lt 1b mBunch Length rms 21 psEnergy Spread rms 02
a at reduced average currentb corresponds to 77 pCbunch
Injector Parameters
USPAS Accelerator Physics June 2013
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
To learn more about Cornell ERL
Two web-sites are available
1) Information about Cornell ERL X-ray science applications other related projects worldwide
httperlchesscornelledu
2) ERL technical memorandum series
httpwwwleppcornelledupublicERL
USPAS Accelerator Physics June 2013
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Bend Undulator Wiggler
endash
endashendash
white source partially coherent source powerful white source
Flu
x [p
hs
01
bw]
Bri
ghtn
ess
[ph
sm
m2
mr2
01
bw]
Flu
x [p
hs
01
bw]
USPAS Accelerator Physics June 2013
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Undulator Radiation from Single Electron
p
N N
N
S
SS
Kz
x
y
zkBB py sin0
]m[]T[493 0 pBK
Halbach permanent magnet undulator
)]81475(exp[333]T[0 B
pgap for SmCo5 here
Approaches1 Solve equation of motion (trivial) grab Jackson and calculate retarded potentials (not so trivial ndash usually done in the far field approximation) Fourier Transform the field seen by the observer to get the spectrum
More intuitively in the electron rest frame2 Doppler shift to the lab frame (nearly) simple harmonic oscillator radiation
3 Doppler shift Thomson back-scattered undulator field ldquophotonsrdquoOr simply
4 Write interference condition of wavefront emitted by the electron
USPAS Accelerator Physics June 2013
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Intuitive understanding of undulator radiation
z
x
endash
in endash frame
pp
d
Pd2sin
N
1
z
x
back to lab frame
1
~
d
dP
1
on a
xis
off-axis
d
dP
1
N
1~
after pin-hole aperture
)1(2
22221
2
Kn
pn
pn nN
1~
(for fixed θ only)
USPAS Accelerator Physics June 2013
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Higher Harmonics Wiggler
z
x
1K
1K
motion in endash frame
z
x1
~even
odd
K le 1 undulatorK gt 1 wiggler
critical harmonic number for wiggler(in analogy to c of bending magnet)
21
4
3 2KKnc
K nc
1 1
2 4
4 27
8 198
16 1548
wiggler and bend spectra after pin-hole aperture
d
dP
log
log
m
eBc 2
3 2 bend
wiggler
2Nspikes
continuum
USPAS Accelerator Physics June 2013
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Total Radiation Power
e
INKKPtot )1(
32
212
1 A][m][
cm][
GeV][726[W]
2
22
ILKE
Pp
tot or
eg about 1 photon from each electron in a 100-pole undulator or1 kW cw power from 1 m insertion device for beam current of
100 mA 5 GeV K = 15 p = 2 cm
Note the radiated power is independent from electron beam energy if one cankeep B0 p const while p ~ 2 to provide the same radiation wavelength (eg low energy synchrotron and Thomson scattering light sources)
However most of this power is discarded (bw ~ 1) Only a small fraction is used
Radiation Neededwavelength 01 ndash 2 Aring (if a hard x-ray source)bw 10-2 ndash 10-4
small source size amp divergence
temporal coherencespatial coherence
USPAS Accelerator Physics June 2013
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Undulator Central Cone
Flux in the central cone from nth harmonic in bw
LnN
K ncen 2
1
2
1 221
Select with a pin-hole aperture the cone
to get bwnNn
1~
n
)(Kge
INN n
nnph
n
Kg
e
I n )(
0
01
02
03
04
05
06
07
08
09
1
0 1 2 3 4 5
Kg
n(K
)
n = 1
3
57
9
)1(
][)(
221
2
K
JJnKKgn
Function
Note the number of photons in bw ~ 1N is about 2 max of the number of endash for any-length undulator
Undulator ldquoefficiencyrdquop
2212
1
)1(
)(3
NKK
Kg
P
P n
tot
cen
USPAS Accelerator Physics June 2013
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
A Word on Coherence of Undulator
r
R
d
L
apparent source disk
c
Radiation contained in the central cone is transversely coherent (no beam emittance)
Youngrsquos double-slit interference condition
~R
rd
Lr c~Rrc ~
Lc ~
in Fraunhofer limit
Spatial coherence (rms) 4 cr
Temporal coherence )2(2 cl clt cc
Photon degeneracy ccphc tN
x-ray source
Rings 1
ERLs 1
XFEL 1
c
Next we will study the effect of finite beam 6D emittance on undulator radiation
same as central cone
USPAS Accelerator Physics June 2013
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Brightness Definition Geometric OpticsBrightness is a measure of spatial (transverse) coherence of radiation Spectral brightness (per 01 BW) is usually quoted as a figure of merit which also reflects temporal coherence of the beam The word ldquospectralrdquo is often omitted Peak spectral brightness is proportional to photon degeneracy
For the most parts we will follow K-J Kimrsquos arguments regarding brightness definitions
A ray coordinate in 4D phase space is defined as
Brightness is invariant in lossless linear optics as well as flux
while flux densities are not
)( )(
yxx
22
4
)(dxd
FdzxB
22)( dxdzxBF
invdzxBxd
FdxdzxB
d
Fd )( )( 2
2
22
2
2
USPAS Accelerator Physics June 2013
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Brightness Definition Wave Optics
here electric field in frequency domain is given in either coordinate or angular representation Far-field (angular) pattern is equivalent to the Fourier transform of the near-field (coordinate) pattern
A word of caution brightness as defined in wave optics may have negative values when diffraction becomes important One way to deal with that is to evaluate brightness when diffraction is not important (eg z = 0) and use optics transform thereafter
xikezEzEdT
cdzxB
)2()2(
2)(
20
yikxx ezyxEzyxEyd
T
cd
)2()2(2
2
20
2
2
2 )( )(1
dezxEExdezxEE xikx
xikx
USPAS Accelerator Physics June 2013
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Diffraction LimitGaussian laser beam equation
With corresponding brightness
)(2)(
1cotexp
)()(
220
0 zR
ik
zwx
z
zkzi
zw
wEzxE
R
)1()( 2220
2Rzzwzw
20wzR
)1()( 22 zzzzR R
2
2
2
2
0
)(
2
1exp)(
rr
zxBzxB
00 1 2 kww rr
Rrr
rr
z
42
0
)2(B
Fcoh 20 )2( rr
FB
USPAS Accelerator Physics June 2013
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Effect of Electron DistributionPrevious result from undulator treatment
The field in terms of reference electron trajectory for ith-electron is given by
For brightness we need to evaluate the following ensemble average for all electrons
2nd term is the ldquoFELrdquo term Typically so only the 1st term is important
)21 ( here ))((e24
)0( 2)(
0
ntnntdc
eE tti
)(i0
i
i
e)0()0( cxtie
eEE
eN
EEEE1i
2i
1i
21 )0()0()0()0(
ji
2j
1i
)0()0(
EE
eN
22
e)1( zkee NN
1e22
zkeN
phase of ith-electron
USPAS Accelerator Physics June 2013
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Effect of Electron Distribution (contd)
)0()0(e)0()0( i2
0
i1
0
)(21
21i
eexik
e EENEE e
)0()0( ii0eee xxBNxB
eeeeeee dxdxfxxBN 220 )0()0(
electron distribution
Brightness due to single electron has been already introduced Total brightness becomes a convolution of single electron brightness with electron distribution function
Brightness on axis due to single electron
2
00
)2()000(
F
B
flux in the central cone
USPAS Accelerator Physics June 2013
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Finite Beam Emittance EffectOftentimes brightness from a single electron is approximated by Gaussian
Including the electron beam effects amplitude and sigmarsquos of brightness become
2
2
2
2
2
00
2
1exp
)2()0(
rr
xFxB
LL rr 2 42
TyTyxTTx
FB
2)2(
)000(
2236122
1212222 LLa xxrTx
2236122
121222 LLyyrTy
222xrxT
222yryT
USPAS Accelerator Physics June 2013
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Matching Electron BeamMatched -function is given by (beam waist at the center of undulator)
Brightness on axis becomes
Matched -function has a broad minimum (for )
x
2 Lrropt
yx
41
41
1
)2()000(
2yx
FB transversely coherent fraction
of the central cone flux
)8(formin2
2formin
2formin2
2
L
L
L
TTacceptable still is 6
4~ if also
Lopt
1)4(or 1)4(
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Energy Spread of the Beam
Energy spread of the beam can degrade brightness of undulators with many periods
If the number of undulator periods is much greater than brightness will not grow with the number of periods
Maximal spectral brightness on axis becomes
20N
22
1
1
41
41
1
)2()000(
NN
FB
yx
USPAS Accelerator Physics June 2013
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
Photon DegeneracyNumber of photons in a single quantum mode
Peak brightness is a measure of photon degeneracy
Eg maximum photon degeneracy that is available from undulator (non-FEL)
2
2
2
tEyx kk
cBpeakc
1
2
3
n
KgNKgNN n
ezyx
ncne
z
nc
)(10 however typicallymore )(
33max
diffraction-limited emittance dominated
USPAS Accelerator Physics June 2013
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-
More reading on synchrotron radiation
1 KJ Kim Characteristics of Synchrotron Radiation AIP Conference Proceedings 189 (1989) pp565-632
2 RP Walker Insertion Devices Undulators and Wigglers CERN Accelerator School 98-04 (1998) pp129-190 and references therein Available on the Internet at httppreprintscernchcernrep199898-0498-04html
3 B Lengeler Coherence in X-ray physics Naturwissenschaften 88 (2001) pp 249-260 and references therein
4 D Attwood Soft X-rays and Extreme UV Radiation Principles and Applications Cambridge University Press 1999 Chapters 5 (Synchrotron Radiation) and 8 (Coherence at Short Wavelength) and references therein
USPAS Accelerator Physics June 2013
- PowerPoint Presentation
- High Field Spectral Distribution
- Slide 3
- Slide 4
- Energy Distribution in Lab Frame
- In the Forward Direction
- Number Spectral Angular Density
- Radiation Pattern Qualitatively
- Dimension Estimates
- Number Spectral Density (Flux)
- Power Angular Density
- Slide 12
- Slide 13
- ERL light source idea
- Coherent or incoherent
- Demand for X-rays
- X-ray characteristics needed
- Introduction
- Introduction (contd) adiabatic damping
- Introduction (contd) storage rings (I)
- Introduction (contd) storage rings (II)
- Introduction (contd) why ERL
- Comparing present and future sources
- 1 Angstrom brilliance comparison
- Cornell vision of ERL light source
- Need for the ERL prototype
- Cornell ERL Prototype
- Cornell ERL Phase I Injector
- To learn more about Cornell ERL
- Bend Undulator Wiggler
- Undulator Radiation from Single Electron
- Intuitive understanding of undulator radiation
- Higher Harmonics Wiggler
- Total Radiation Power
- Undulator Central Cone
- A Word on Coherence of Undulator
- Brightness Definition Geometric Optics
- Brightness Definition Wave Optics
- Diffraction Limit
- Effect of Electron Distribution
- Effect of Electron Distribution (contd)
- Finite Beam Emittance Effect
- Matching Electron Beam
- Energy Spread of the Beam
- Photon Degeneracy
- More reading on synchrotron radiation
-