measuring high brightness beams
TRANSCRIPT
Measuring high brightness beams
C.Limborg-Deprey
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 2
Introduction
Measuring e-beam properties
emittance, charge, monochromaticity, pulse duration β¦
π΅ = π
νπ,π₯ νπ,π¦ νπ,π§
π΅ = π
νπ,π₯2 ππππΈ
Standard measurement techniques for tuning FELs
Some measurements of ultimate beam dimensions for colliders
and e-diffraction sources
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 3
Synopsis
β’ Emittance definition
β’ Transverse emittance measurements
β’ Beam size measurements
β’ Destructive
β’ Non-Destructive
β’ Bunch lengths
β’ Non-Destructive
β’ Destructive
β’ Longitudinal Phase space
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 4
6D-emittance
Evolution of a population of particles (~109 for 160 pC) in time
3D-space coordinates (x, y, z) and their canonical (Hamilton) conjuguates (ππ₯,py, ππ§)
6D phase space of non-interacting particles,
in a conservative dynamical system
is invariant
βLiouville theoremβ
Volume π = π(π₯, ππ₯, π¦, ππ¦, π¦, π§, ππ§) ππ₯ πππ₯ ππ¦ πππ¦ ππ§ πππ§ conserved
V referred to as emittance
J.D.Lawson βThe physics of charge particle beams β , Clarendon Press, Oxford, 1977
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 5
6D-emittance β more practical choice of coordinates
Particles travel along z with relativistic velocity π£ = π½π and ππ§ = π½πΎπππ
then ππ₯ = π£π₯πΎππ =ππ₯
ππ§
ππ§
ππ‘πΎππ = π₯β²π½π πΎππ
ππ₯ β ππ₯ππ§π
= π₯β²
ππ¦ β ππ¦
ππ§π= π¦β²
π§ β π§ β π§ππ½π
= π
ππ§ β πΏ =ππ§βππ§πππ§π
or πΏ =πΈβπΈπ
πΈπ
(x,xβ) are the trace-space coordinates (not conjuguate quantities)
π₯, ππ₯ , π¦, ππ¦, π¦, π§, ππ§ (π₯, π₯β², π¦, π¦β², π,πΏ) (measured quantities)
z
ππ§π for centroid
subtleties of emittance conservation are discussed in K.Floettmann , βsome basic features of
the beam emittanceβ PRST-AB Vol.3, 034202 (2003)
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 6
Geometric emittance / Normalized emittance
ν = π(π₯, π₯β², π¦, π¦β², π, πΏ) ππ₯ ππ₯β² ππ¦ ππ¦β² ππ ππΏ
e geometric emittance
e conserved in the absence of acceleration
(e decreases with 1/ g3 when beam accelerated)
we introduce en = g3 e , normalized emittance en
en conserved in the presence of acceleration
--------------------------- Possible sources of emittance growth ------------------------------
Non-linear space charge forces
Non-linear forces from electromagnetic components
Synchrotron radiation emission
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 7
Emittance - Practical evaluation
2D emittance : area occupied by particles represented in 2D βtrace spaceβ
What is the βareaβ for points ?
arbitrarily define a contour
Typical distributions are gaussians,
or if not,
can be evaluated by their rms value ,
< π’2 > ,< π’β²2>,< π’π’β² >
u
uβ
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 8
Emittance - Practical evaluation
β’ Determinant of the matrix of second order moments
< π’2 > < π’π’β² >
< π’π’β² > < π’β²2>
1/2
ν = < π’2 >< π’β²2 >β< π’π’β² >
Corresponds to ν = π΄
π= ππ ππ
β’ Another definition : βLapostolleβ
ν = 4 < π’2 >< π’β²2 >β< π’π’β² >
Corresponds to π΄β
π= 2ππ 2ππ
u
uβ
used in our
community
u
uβ
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 9
Emittance
Define Twiss parameters π½, πΌ, πΎ by
< π’2 > = π½ν
< π’β²2 > = πΎν
< π’π’β² > = βπΌν
π½, πΌ, πΎ define the orientation of the ellipse
πν defines the area
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 10
Courant-Snyder
Another approach to emittance
Particles (u,uβ) subject to restoring forces K(s) u
π’β²β² + πΎ π π’ = 0 Hillβs equation
Solution: π’ π = νπ½ π π ππ π π + ππ
with π π = ππ β²
π½ π β²
π
π π
ν and ππ are constants of integration
Defining : πΌ π = β1
2π½β² π and πΎ π =
1+πΌ2 π
π½2 π
πΎ π π’2 π + 2πΌ π π’ π π’β² π + π½ π π’β²2 π = constant (Courant-Snyder Invariant) = e
Also equation of an ellipse
Explains why choice of an ellipse is more than a mathematical convenience
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 11
Measuring emittance
ν = < π’2 >< π’β²2 >β< π’π’β² >
Beam size Beam divergence Correlation
Position-angle
One method gives the 3 parameters in one shot : βPepper potβ
but
destructive
only for low energy beam (E < 10 MeV)
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 12
Direct reading of trace space
π’β²π = π₯β²π =π’π β π₯π
πΏ=π’π βππ
πΏ
πβ²π2= ππ’,π
2 β π
4
2
< π₯2 > = πΌππ₯π
2
πΌπ ,
< π₯β²2> =
πΌπ π₯β²π,π2 +
πβ²π2
πΏ2
πΌπ ,
< π₯π₯β² > = πΌππ₯π,ππ₯β²π,π
πΌπ
With Im detected intensity for mth beamlet
Pepper pot
Transverse emittance , low energy
Destructive
Single Shot
M. Zhang, Report No. FERMILAB-TM-1988, 1996
S. G. Anderson, et al. Phys. Rev. ST Accel. Beams 5, 014201 (2002)
u Multislit in high Z material
ππ’,π
d a
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 13
Pepper pot for thermal emittance
C.P Hauri , PRL 104, 234802 (2010)
Electron beam on YAG, with pepper pot in, Solenoid scan
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 14
Pepper pot based emittance oscillation
D.Alesini et al , βExperimental results with the
SPARC emittance-meterβ MOOAAB02, PAC07
Emittance-meter
Variation of emittance along z after gun (at 5 MeV)
2mm thick W
7 slits of ~ 50 mm at 500 mm
Resolution ~ 100 mrad PITZ data
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Photofield emission from tips : Nb/ Nb3Sn
A.Anghel et al , PRL , 108, 194801 (2012)
No explosive electron emission erosion
even if close to 1GW/cm^2 limit
Huge QE ~ 0.9 % (X 100)
en = 0.6 mm-mrad at 2500pC
Brightness better by ~ 100
than conventional PC guns
14326 filaments, f = 3.8 mm
2 laser spots
50 mm 100 mJ/cm2
160 mm 10 mJ/cm2
for 2 mJ , 6ps 266 nm laser
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 16
Pepper pot
β’ Difficult at high energy
scattering stopping length longer with energy :
πΏπ [ππ] =πΈ
ππΈππ₯ β
πΈ[πππ]
1.5 π π.ππβ3
E > 10 MeV , Ls ~ 5 mm
β’ Unsuitable for extremely low emittance
slit thickness condition : ππ₯β² <π
4π€
minimum emittance β a (slit width) but S/N decreases
β’ Space Charge correction: low energy : analysis still often requires
space charge calculation
G. Anderson, et al. Phys. Rev. ST Accel. Beams 5, 014201 (2002)
a
w
Transverse emittance , low energy
Destructive
Single Shot
W Ta Cu
[g/cm3] 15.6 16.7 8.96
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 17
Measuring extremely low emittance <0.1 mm-mrad
Grid technique similar to pepper pot ,
multi knife edge measurement with info. on correlations
electrons hitting Cu bars scattered at wide angle
huge magnification M= 12.8 (from L =2 m)
M a > L sβm
a : bar width = 32 mm
L : distance grid to screen =2.1m
sβm : divergence of beamlet ~40 mrad
Grid for low emittance
Transverse emittance , low energy
Destructive
Single Shot
R.Li et PRST-AB 15, 090702 (2012) 30nm measured with 0.1 pC
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 18
Studying cigar shape :
linear space charge
R.Li et PRST-AB 15, 090702 (2012)
Grid for low emittance
Transverse emittance , low energy
Destructive
Single Shot
1.8ps
65fs
GPT Simulations Profile measured
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 19
Quadrupole/solenoid scan
π₯π₯β²
= 1 πΏ0 1
1 0
β1
π1
π₯ππ₯β²π
= π π₯ππ₯β²π
π₯ = 1 βπΏ
ππ₯π + πΏπ₯π
π₯β² = βπ₯ππ+ π₯β²π
π₯2 = 1 β2πΏ
π+πΏ2
π2π₯π2 + 2πΏ 1 β
πΏ
π π₯ππ₯β²π + πΏ2 π₯β²π
2
π₯2 =π
π2+
π
π+ π
Solve for a,b,c to determine π₯π2 , π₯ππ₯β²π , π₯β²π
2
ν = π₯π2 π₯β²π
2β π₯ππ₯β²π , πΌ = β
π₯ππ₯β²π
ν , π½ =
π₯π2
ν , πΎ =
π₯β²π2
ν
βQuadβ scan
Transverse emittance
Destructive
Multi Shot
lens , f 1
π= βπΎπ
drift , L
βScreenβ
(YAG, OTR,
wire scanner)
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 20
ππ₯12
ππ₯22
β¦β¦ππ₯π2
=
π 11,12 2π 11,1π 12,1 π 12,1
2
β¦β¦β¦
β¦β¦β¦
β¦β¦β¦
π 11,π2 2π 11,ππ 12,π π 12,π
2
π½πνβπΌπνπΎπν
also written Ξ£ = π΅π
Solve for O by least square fit
Minimization of π2 = 1
ππ₯π2 ππ₯π
2 β π΅πππ ππ2
π
Error analysis
Calculate covariant matrix π = π΅ ππ΅ β1
where π΅ ππ =π΅ππ
ππ₯π2
Solution is π = ππ΅ πΞ£ where π΅ ππ =π΅ππ
ππ₯π2 and Ξ£ π = ππ₯π
2
Error ππ,π = πππ
βQuadβ scan
Transverse emittance
Destructive
Multi Shot
Reference βF.Zimmermann, M.Minty, β book ref. H.Loos , private communications
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 21
β’ Choice of quadrupole settings
At each data point , plot lines parametrized in xβi
π’
π’β²= π
ππ₯ππ₯β²π
Optimum location of data points
over-constrain (N points > 3)
at least 3 separated by more than 45 degrees
typically ~ 7 points , covering more than 90 degrees
β’ Convenient representation in normalized/rotated phase
space
π₯
π½,πΌπ₯+π½π₯β²
π½ where πΌ, π½ Twiss design parameters
βQuadβ scan
Transverse emittance
Destructive
Multi Shot
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 22
β’ Low energy or high density
strong space charge,
R to include space charge defocusing term (beam size dependent)
Use iterative methods
βQuadβ scan
Transverse emittance
Destructive
Multi Shot
C.K. Allen βTheory and Technique of Beam Envelope Simulationβ, LANL, LA-UR-02-4979 August 2002
C.Limborg, βA Modified Quad Scan technique for space charge dominated beamsβ, PAC03 ,
http://accelconf.web.cern.ch/AccelConf/p03/PAPERS/WPPG033.PDF
Rsc (Ds)=
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 23
Slice emittance
Slice emittance
Destructive
Multi Shot
e-
sz
sy Transverse
deflector
Projects time
into space
e-
sz
sy Quadrupole
x-focusing
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013
Slice emittance
Slice emittance
Destructive
Multi Shot
TAIL
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 25
β’ Thermal emittance measurement from slice emittance as a function of laser spot size (at
low charge ~20pC)
β’ LCLS gun : copper (robustness, long lifetime)
β’ 0.9 mm-mrad per mm rms from slice emittance measurement
Thermal emittance
Transverse emittance
Destructive
Multi Shot
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 26
β’ Thermal emittance measurement from photoinjector
Thermal emittance
Transverse emittance
Destructive
Multi Shot
Courtesy F.LePimpec, R.Ganter
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 27
Thermal emittance
C.P Hauri , PRL 104, 234802 (2010)
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 28
νπ = ππ₯πππ₯
ππ for e-source
νπ = ππ₯πππ
ππ2 transverse velocities expressed in terms of temperature
Typical numbers for photo-injectors (metallic or semi-conductor):
νπ = 0.9 ππ βππππ πππ ππ πππ
T = 4809 K , πππ = 0.41 ππ
FELs, linear colliders : small beam size collimated beam
βgeometric emittanceβ ν =νπ
πΎ small at high g and small νπ
For electron diffraction community, coherence length
πΏπ =π
2πππ =
β
ππ ππ₯
ππ,π₯ Lc needs to be many lattice spacing
example: νπ = 0.02 ππ βππππ
ππ₯ = 0.2 ππ
Quality of source measured in πΆβ₯ =πΏβ₯
ππ₯
Emittance , Temperature , Coherence Length
Lc = 4 nm
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 29
Cold Electron source
Courtesy O.J.Luiten
N ~ 108 Rb atoms
R = 1mm
T = 230 mK
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 30
Cold Electron source
Courtesy O.J.Luiten
20K
νπ = ππ₯πππ
ππ2
π β‘ππ2
πππ
T = 5000 K for 0.9 mm-mrad per rms mm
T = 1500 K for 0.5 mm-mmrad per rms mm
Conventional photo and field
emission fields
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 31
Solenoid scan
Engelen et.al Nature Communications βHigh-coherence electron bunches produced by femtosecondβ
Engelen et al βEffective temperature of an ultracold electron source based on near-threshold Photoionizationβ
Solenoid scan
for extremely small emittance
Courtesy O.J.Luiten
πππ~20 ππ controlled by ionization laser
Energy measured with Time of Flight from ionization laser (photodiode) to screen
0.4 fC measured on Faraday Cup (~ 3000 particles)
MCP-phosphor screen (photo-multiplication) for enhancing signal for single
electron detection
Pinhole for resolution determination ~100mm
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 32
Solenoid scan
for an extremely small emittance
Transverse emittance , low energy
Destructive
Multi Shot
Courtesy O.J.Luiten
Engelen et.al Nature Communications βHigh-coherence electron bunches produced by femtosecondβ
Engelen et al βEffective temperature of an ultracold electron source based on near-threshold Photoionizationβ Ultramicroscopy
ν = 1.4ππ for Q =0.5 fC ( ~3000
particles)
Equivalent to 70 nm-rad per mm rms
~ 10 times smaller than RF photoinjectors
So 100 times larger brightness
Main conclusion
fs-ionization still allows to reach 20K thermal
emittance
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 33
Spatial projection : choice of βscreensβ
Very good physics description of physics E.Bravin in
http://cds.cern.ch/record/1071486/files/cern-2009-005.pdf
Screens
ZnS phosphor screens
small dynamic range , easily saturated
grain size ~ 20mm
response time
YAG screens :
good yield
thickness
response time
Scintillator properties : http://scintillator.lbl.gov/
YAG combined with MCP for low electron density
OTR screen
Wire scanner
Ultimate wire
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013
β’ Emitted when a relativistic electron passes boundary between
materials of different electrical properties
β’ OTR emission from a single electron
β’ Travelling with relativistic velocity π½ β 1 β1
2πΎ2
β’ Hitting a foil with reflectivity π π foil
β’ Typically at 45 degrees w.r.t to beam direction
β’π2π
πππΞ©=
πΌ
4π2π π
π
π½2π ππ2 π
1βπ½πππ π2
34
OTR (Optical Transition Radiation)
Ο = 45Β°
e-beam
foil
ΞΈ
π > 150 ππππ , 60% ππ πππβπ‘
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 35
OTR far-field imaging
Simulations P.Piot , 38 MeV
resolution π₯β²~ 0.15
πΎ
(too poor for high brightness beams)
but accurate energy measurement
Deconvolution of e-beam divergence
with single e angular distribution
OTR interferometry
Back TR from 1st foil
Distance between 2 foils > ππΎ2
R.Fiorito OTR-ODR interferometry π₯β²~ 0.02
πΎ
resolution π₯β²~ 0.075
πΎ
Can we do far-field imaging and obtain the e-beam divergence ?
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013
β’ Calculate Nphotons
β’ Spectral reflectivity of foil (Al,Ti, Be,Si)
β’ Spectral sensitivity of imaging system (lens, CCD)
β’ π ππ , ππ = π π
ππ π ππ
ππ
ππ
π π
πππ =
ππ
ππlogπ
ππ=400ππ
ππ=700ππ = 0.56
36
OTR (Optical Transition Radiation)
Quantum Efficiency
from Sony ICX445
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013
Beam size : βpoint-to-point imagingβ
Point Spread Function (PSF) : single e emission (Greenβs) through imaging system
πππΉ β π π₯, π¦ (for incoherent emission)
Example:
50 mm, 1:1 imaging ,100pC , 70 MeV
Collection angle = 100mrad
BW=0.7, QE = 0.5
Nelectrons ~2.106
Disk with 1.5 rms contains 70% of particles
With pixel size (3.75 mm)2 , ~ 1000 e per pixel
NB: full well capacity 30000,
With 8 bits above noise => noise level at 100e
~ 10 pC
37
Imaging using OTR light
Tight
Alignment
tolerances
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013
β’ PSF βPoint Spread Functionβ: response of imaging system to a point source
β’ Incoherent: πΌππππ π1 + π2 = πΌππππ π1 + πΌππππ π2
πππΉ β π π₯, π¦ => πππ‘πππ ππ‘π¦ β ππ
β’ Coherent: image formation linear in complex field
In short πΉπβ1 πΈπ ππ₯ , ππ¦ Γ π ππ₯ , ππ¦
π¬ π =π
ππ£
π
ππΌπΎ1 πΌπ electric field at the transition radiation source with πΌ =
π
π½πΎ
πΈπ,π π = πβπππ§π πΈπ π π β ππ
π¬π,π π2= π π2 πβ² ππ§ π πβ², π§ π¬π,π π β πβ²
2
+ π2 π2 πβ²ππ§ πβπππ§ π πβ², π§ π¬π,π π β πβ²2
β’ Microbunching generates phase relations for particles along bunch making the N2 component
large and dominant
38
OTR (Optical Transition Radiation)
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013
Coherent emission:
OTR image show square of gradient of shape
thus the βdoughnutβ shape
Spoils measurement of rms beam size (under estimate)
Starts from shot noise => present in continuous spectrum
39
Coherent OTR (COTR)
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013
COTR suppression:
Smearing out microbunching
Spectral separation: imaging for π < ππ (ie extreme UV, in vacuum)
Spatial separation: Use scintillator screen , tilted to avoid COTR
Temporal separation: (scintillator response ~ 70 ns) with expensive
ICCD
Use Phase retrieval algorithm (A.Marinelli) on far-field COTR
40
OTR for beam size measurement
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 41
Beam size measurement despite COTR
Far Field
COTR
|B (kx,ky) | Phase{B (kx,ky) }
A,Marinelli et al .
PRL 110, 094802 (2013)
No-microbunching
Direct OTR imaging
Reconstructed image
(beam is micro-bunched)
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 42
Small wire intercepts beam
Bremsstrahlung radiation and scattered electrons detected on fast ion chambers with PMTs
(PMT = Photo-Multiplying tubes)
detecting Cerenkov from secondary electrons
light from plastic scintillator fibers along chamber
Positioned at low background location
Material
W more signal but burn more easily ~ 20-40 mm
C less signal , but more robust can go down to few mm
for a 4 mm rms beam sizes down to 1 mm can be measured
Major issues
break (high rep. rate and high Ipeak) 2nC in wire of 1 mm
vibrations
beam jitter (from magnet power supplies stability)
Wire scanner Non-destructive beam size
Multi Shot
H.Loos , MOIANB01 Proceedings of BIW10, Santa Fe, New Mexico, US
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 43
Wire scanner Non-destructive beam size
Multi Shot
H.Loos , MOIANB01 Proceedings of BIW10, Santa Fe, New Mexico, US
β’ Vibrations are a limitation
resonance studies : speed tests
optical measurements
SLAC PUB-6015 McCormick, M.Ross
Mechanical improvements to reduce further
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 44
Compton scattering process
Collision photons with relativistic electrons
Scattered photons
β’ Direction : in cone with opening angle in 1/πΎπ
β’ Frequency : Doppler shifted
βππ π = βπππΎππΈπ 1βπ½ππππ π
πΎππΈπ 1βπ½ππππ π +βππ 1βπππ πβπβ 2πΎπ
2βππ for π βπ
2
β’ Intensity :
ππ π β ππ ππ ππππππ‘ππππ π· π€ππ‘β ππ =1
βππ π
π
π
(π, π) βΆ ( πππ€ππ, π πππ‘ π ππ§π ) ππ πππ ππ π· βΆ πππ π‘ππππ ππ πππ‘πππππ‘πππ
ππ βΆ πΆππππ‘ππ ππππ π π πππ‘πππ β 6.6 10β29π2
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 45
β’ measure e-beam sizes > 200nm,
β’ high current beams
(βnon-degradableβ wire )
β’ detection of X-Ray (or g-rays)
or recoil energy (for very high Ee-beam)
β’ scan either laser or e-beam position
β’ detection requires bending magnet
β’ challenges
synchronization
focus
scan
Laser wire scanner
Non-destructive
Non-degradable
Multi Shot
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 46
β’ Measurements SLC
(pioneering experiment)
E = 45 GeV,
Nphotons at waist ~ 8000
Bunch size measured ~ 1mm
Laser wire scanner
Non-destructive
Non-degradable
Multi Shot
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 47
β’ Focus:
Diffraction limit of a laser beam ππ =π π
4πππππ ππ,πππ
Rayleigh length π§π =4πππ
2
π
Example: ππ ~125nm , π§π ~ 625 nm for π = 300nm
Beam size measurements limited to ~ 200nm
Applications : ERL, linear colliders
Other application: bunch length measurement
Laser wire scanner
Non-destructive
Non-degradable
Multi Shot
,
References:
Shintake, Tennenbaum , Annu. Rev. Nucl. Part. Sci. 1999. 49:125β62
Lefebvre https://cds.cern.ch/record/535808/files/open-2002-010.pdf
A.Murohk, IPAC10 βA 10 MHZ Pulsed Laser Wire scanner for energy recovery linacsβ
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 48
Beam size from
laser interferometer
Non-destructive
Non-degradable
Multi Shot
β’ measure e-beam sizes < 200nm, by beating the diffraction limit using interferences
β’ ππΎ = π΄ + π΅ πππ 2ππΏπ₯ + π
β’ ππΎ π¦π =ππ
21 + πππ 2ππΏπ¦π πππ π exp
β2 ππ¦ππ¦2
β’ πΒ± =ππ
21 Β± πππ π exp
β2 ππ¦ππ¦2
β’ π = π+βπβ
π++πβ
β’ ππ¦ =π
2π2ππ
πππ π
π
With π = 174Β° , ππ¦ down to 38 nm can be measured
with a 1mm laser
βShintake-monitorβ
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 49
Beam size from
laser interferometer
Non-destructive
Non-degradable
Multi Shot
Courtesy Jacqueline Yan,KEK
β’ Systematics
β’ Imbalance power between 2 arms
β’ Variation in e-beam angle
β’ Longitudinal extent of diffraction
pattern
β’ Spherical wavefront error
β’ Coherence of laser (transverse +
longitudinal)
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 50
Beam size from
laser interferometer
Non-destructive
Non-degradable
Multi Shot
β’ Shintake pioneering measurement SLAC (1994)
β’ KEK measurements
Courtesy Jacqueline Yan,KEK,
1.3 GeV, π = 174Β° Very reproducible over 20 minutes
M γ 0.306 ie Οy γ 65 nm
Best measurement Οy γ 58 nm
Goal = 37 nm
E = 46.6 GeV Οy γ 77 nm
T.Shintake, P.Tenenbaum, Annu. Rev. Nucl. Part. Sci. 1999. 49:125β62
http://www.jlab.org/accel/beam_diag/DOCS/annurev.nucl.49.1.125.pdf
1.6nC
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 51
Optical Diffraction Radiation
Interferometry (ODRI) Non-destructive
For single shot x,xβ
A.Cianchi Journal of Physics: Conference Series 357 (2012) 012019
http://prst-ab.aps.org/pdf/PRSTAB/v14/i10/e102803
β’ 0.4nC * 20 bunches at 5Hz ~ 80nC enough to damage OTR
β’ 2 apertures at d < ππΎ2 (βformation lengthβ) but with different aperture size
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 52
Optical Diffraction Radiation
Interferometry (ODRI) Non-destructive
For single shot x,xβ
A.Cianchi Journal of Physics: Conference Series 357 (2012) 012019
http://prst-ab.aps.org/pdf/PRSTAB/v14/i10/e102803
β’ Calculation Measurements
ππ¦ = 81ππ, ππ¦β² = 203 ππππ
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 53
βsingle pointβ emittance
measurement Destructive or non-destructive
Single Point
π₯ = 1 β
πΏ
ππ₯π + πΏπ₯π
π₯β² = βπ₯π
π+ π₯β²π
π₯2 = 1 βπΏ
π
2π₯π2 + 2πΏ 1 β
πΏ
π π₯ππ₯β²π + πΏ2 π₯β²π
2
π₯π₯β² = β1
π1 β
πΏ
ππ₯π2 + 1 β
2πΏ
π π₯ππ₯β²π + πΏ π₯β²π
2
Find magnet setting f* such that π π₯2
ππ= 0
then correlation term π₯π₯β² =π₯2
πΏ
at f* , measure π₯2 , and deduce π₯π₯β²
measure π₯β²2
emittance at single point
(with 2 images : one near-field, one far-field)
e-beam f
L screen
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 54
BUNCH LENGTHS
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 55
Electro-Optic methods Bunch length
Non-destructive
πΈπ component of Lorentz contracted Coulomb field
Birefringence induced by πΈπ , π = νπ ππ(0) πΈ + ππ
(1) πΈ2 +β―
Pockels Kerr
Changes polarization and introduces phase retardation
As an E-field pulse mixer, casually referred to as an βultrafast Pockels cellβ
2
πΎ
πΈπ πΈπ
500 MeV (g = 1000)
r = 5mm
L = 10 mm = 33 fs
r
L
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 56
Electro-Optic Sampling
Bunch length
Non-destructive
Multi Shot
1. Laser pulse much shorter than e-beam pulse used as probe
β’ Samples small part of e-beam field
2. Analyzer (polarizer) to transmit polarization change to photo-diode
3. Scan delay to trace out e-beam profile
Limitation as multi-shot method:
β’ Shot-to-shot timing jitter bad for profiling
β’ (Still useful time of arrival monitor)
from Bernd Steffen,
DESY
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 57
Electro-Optic spectral decoding
Bunch length
Non-destructive
Single Shot
1. Laser pulsed stretched: long chirped laser with linear Ξ»-t correlation
2. Interaction with πΈπ from e-beam in EO induces t-dep. change in polarization
3. Analyzer/spectrometer measures change in polarization as function of Ξ»
4. Map Ξ» back to t to deduce e-beam profile
Limitation from non-linear optical mixing:
β’ Resolution tres worsens with increasing chirp duration βwindowβ Tc as
Typ. temporal resolution > 200fs
from Bernd Steffen,
DESY
cpres TTt
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 58
Electro-Optic temporal decoding
Bunch length
Non-destructive
Single Shot
β’ Similar to before but pulse is decoded in
time-domain
β’ Decoding setup similar to fast, optical
cross-correlator
Limitations: again, gate width
thickness of BBO
spatial resolution
from Bernd Steffen,
DESY
πΌππ»πΊ π₯ = πΌπππππ π‘ + π + πΌπππ‘π π‘ ππ‘
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 59
Electro-Optic temporal decoding
Bunch length
Non-destructive
Single Shot
Temporal resolution achieved ~ 60 fs
Benchmarked with transverse deflector measurements
G.Berden , PRL , 99, 164801 (2007)
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 60
Electro-Optic spatially resolved Bunch length
Single Shot
A.L Cavalieri PRL 94, 114801 (2005)
Resolution ~ 115fs rms
B.Steffen PhD manuscript,
C.Casalbuoni , PRST-AB, 11, 072802 (2008)
T.Maxwell http://www.niu.edu/physics/_pdf/academic/grad/theses/Maxwell_2012.pdf
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 61
Electro-Optic limits Bunch length
Single Shot
C.Casalbuoni , PRST-AB, 11, 072802 (2008)
Maximize signal but minimize crystal size given all the broadening contributions
TO : Transverse Optical phonons limit bandwidth
GVM: Group Velocity Mismatch
(signal and probe slip through each other)
GVD : Group Velocity Dispersion
(signal and probe broaden)
H.Tomizawa, BIW 2012
Organic crystal DAST, compared to ZnTe
Both crystals are 2mm from beam , and 280 pC
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 62
3D βmonitor Tomizawa
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 63
3D Monitor Tomizawa
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 64
Transverse deflector (TCAV)
Bunch length
Destructive
Single Shot
Resolution :
ππ¦2 = νπ½πππ + π½πππ π½ππΆπ΄πππ§
2ππππππ
πΈπ ππΞπ
2
ππ§ >
ν
π½ππΆπ΄π
ππππΈ
2ππππ
Ξπ¦ = π½πππ π½ππΆπ΄π sinπππππ£βπππ ππππ ππ ππππ§ + πππ
ππ
Ξπ¦β² π§ =πππππ
π ππ(ππππ§ + πππ)
TM11 mode
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 65
Transverse deflector (TCAV)
Bunch length
Destructive
Single Shot
ππ πΉ[Β°] 80 90 100
Be
am
po
sitio
n (
pix
el)
1- calibration at zero crossing : 1Β° π πΉ π‘π πππ₯ππ
1Β° π πΉ π β π΅πππ = 1ππ 1Β° π πΉ π β π΅πππ = 250 ππ
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 66
Transverse deflector (TCAV)
Bunch length
Destructive
Single Shot
Deconvolve beam size contribution
ππ πΉ = β90Β°
ππ πΉ = +90Β°
ππ πππππ
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 67
LCLS bunch length measurements
14 GeV
βMaxβ Compression
0.89 ps
14 GeV
135 MeV
1.10 mm rms
14 GeV
BC1 Design Compression
10.3 ps
135 MeV
97 A 950 A 520 A
1.7 ps
14 GeV
PR55 OTR2 135 MeV
14 GeV
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 68
Transverse deflector (TCAV)
Bunch length
Destructive (*)
Single Shot
Resolution : ππ§ >πΎππ
π½ππΆπ΄π πππ
πππ πππ
2
2π
(*) pulse stealing on LCLS (1Hz for a 120Hz operation)
Resolution Tech P[MW]
V[MV]
L[m] E[MeV] e [mm-
mrad]/b [m]
Loc.
250 fs S-Band (1) 0.5/0.7 0.4 135 0.3/5 LCLS inj.
11 fs (3) S-Band ?/15 2.44 5000 0.5/60 LCLS main
33 fs X-Band (2) 1/? 0.13 100 1/11 XTA
1 fs X-Band 40/? 2.0 4300 LCLS dump
3 fs X-Band 40 /? 2.0 14000 LCLS dump
(1) S-Band is 2.856 GHz (2) X-Band is 11.424 GHz (3) Measured on wire scanner
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 69
Transverse deflector (TCAV)
Bunch length
Destructive
Single Shot
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 70
Longitudinal Phase space Destructive (but βstealing modeβ )
Single Shot
e-
sz
2Γ1 m RF βstreakβ
Dipole
X-band RF deflector
ener
gy
Undulator
D 90Β°
bd bs
XTCAV streaks horizontally;
Dipole bends vertically.
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 71
Longitiudinal Phase space
Bunch length
Destructive
Single Shot
Data taken on June 4th, 2013.
Beam energy 3.5GeV, 150pC.
Temporal resolution is about 1.7fs
rms in this test.
Preliminary results.
Lasing
suppressed
Full lasing
Initial Measurement of e-beam and X-ray temporal profiles at LCLS using X-Band
transverse deflector
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 72
Longitudinal Phase space end LCLS injector
Z.Huang, Phys. Rev. ST Accel. Beams 13, 020703 (2010)
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 73
Acknowledgments
C.Pellegrini, D.Xiang, T.Raubenheimer
H.Loos, T.Maxwell, M.Ross, D.McCormick, G.White,
A.Marinelli, Y.Ding, P.Emma, P.Krejcik, J.Wu
J.O.Luiten, J.Yan, F.LePimpec, R.Gantry, F.Zimmermann,
M.Minty , S.Anderson, C.Hauri, A.Anghel, B.Steffen,
B.Schmidt, A.Cianchi, A.Cavalieri, R.Li, W.Engelen,
R.Fiorito, K.Rezaie, A.Nause, T.Shintake, P. Tenenbaum,
D.Dowell, G.Berden, C.Casalbuoni, H.Tomizawa,
β¦
and all the students
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 74
Topics of interest
β’ Tomography
β’ Optical Replica
β’ Synchronization
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 75
Electro-Optic Sampling
T.Maxwell
http://accelconf.web.cern.ch/accelconf/IPAC2011/papers/tup
c169.pdf
http://www.niu.edu/physics/_pdf/academic/grad/theses/Max
well_2012.pdf
B.Steffen
http://fla.desy.de/projects/eo/index_eng.html
http://www-library.desy.de/cgi-bin/showprep.pl?thesis07-020
Casalbuoni
http://prst-ab.aps.org/pdf/PRSTAB/v11/i7/e072802
Bunch length
Non-destructive
Single Shot
C.Limborg-Deprey, SLAC, SSSEPB July 24th 2013 76
Synchronization (AOS-based)
Cavalieri
http://prl.aps.org/abstract/PRL/v94/i11/e114801
Non-destructive
Single Shot