problem: determination of optimal compression of bc1 and bc2 and longitudinal feedback system....

PROBLEM:Determination of optimal compression of BC1 and BC2and longitudinal feedback system .

PROPOSED SOLUTION: Power monitor of CSR emitted from compressors

•Pyroelectric detector measures the CSR power in THz region.

•The emitted power increases as the bunch gets shorter.

•RF accelerating phases before compressor are changed to find the optimal compression.

•Applications to longitudinal feedback system

References:TTF2 Linac- Y.Kim et al. FEL2005 pg 518LCLS Linac - J.Wu et al. SLAC-PUB- 11275 and11276 May, 2005

M.Veronese, M.Ferianis

Radiation sources for diagnostic purposes: signals evaluation for FERMI

+COHERENTRADIATION EMISSION

ShortBunches

•Synchrotron Radiation

•Transition radiation

•Diffraction Radiation

I N particles I N2 particles

•d2 I/dd tot = [N+N(N-1)|F|2] d2 I/dd single e–

•|F|2 = |dr (r)e-irk|2 Coherence enhancement factor:

|Fourrier Transform of longitudinal electron distribution|2


Medium Bunch Long Bunch

S. Di Mitrisimualtions

after BC1

after BC2

at LINAC end

Enhancement factors:

medium bunch long bunch


Comparison between step function and expected bunch

The peaks enhance high frequencies


Synchrotron Radiation angular spectral distribution

References:H.Wiedemann “Particle Accelerator Physics” SV, NY 1993O.Grimm single electron synchrotron radiation emission from TTF2-BC2

Integrating over the solid angle:


Incoherent Synchrotron spectrum for medium and long bunches


CSR spectra for expected MEDIUM bunch @(BC1,BC2)

gau

ssia

n

gau

ssia

n

VIS

IBL

E

VIS

IBL

E


gau

ssia

n

gau

ssia

n

CSR distributions for expected LONG bunch @(BC1,BC2)

VIS

IBL

E

VIS

IBL

E


Vacuum Chamber low frequency cut-off

Warnock PAC1991 pg1824: 2 Parallel perfectly conducting planes

cutoff =2*h3/2/R1/2

shielding function

Dohlus and Limberg NIMPR-A v407 pg278 y1998


CSR shield from 2 Perfect conduct. planes: cutoff< < bunch,

cutoff =2*h3/2/R1/2

bunch=2**z (z =rms bunch length)-gaussian approximation

location/

bunch type

R[m] h[m] cutoff/cutoff bunch/bunch RMS LB[m]

exit BC1

medium

7.38 0.01

0.02

0.03

0.74[mm]-0.41[THz]

2.08[mm]-0.14 [THz]

3.8[mm]-0.078 [THz]

2[mm]-0.144[THz] 1.1 [ps]

0.33 [mm]

exit BC1

long

7.38 0.01

0.02

0.03

0.74[mm]-0.41 [THz]

2.08[mm]-0.14 [THz]

3.8[mm]-0.078 [THz]

4.5[mm]-0.067 [THz] 2.4 [ps]

0.71 [mm]

exit BC2

medium

9.35 0.01

0.02

0.03

0.65 [mm]-0.46 [THz]

1.85[mm]-0.16 [THz]

3.4[mm]-0.088 [THz]

0.59[mm]-0.506 [THz]

0.31 [ps]

0.094 [mm]

exit BC2

long

6.17 0.01

0.02

0.03

0.80[mm]-0.37 [THz]

2.30[mm]-0.13 [THz]

4.2[mm]-0.072 [THz]

1.5[mm]-0.197 [THz] 0.8 [ps]

0.24 [mm]


Proposed layout for BC1/BC2 CSR THz extraction

TTF2 design adapted to FERMI BC1: -bigger chamber height -> 30 mm-CSR detection ->no transport line-> as near as possible pyroelectric detector to avoid water absorption-angle of extraction 0.045rad


Angular distribution for CSR extraction from BC1 e BC2.

For low frequencies <<c the angular distribution becomes wider.The critical angle at which the SR decrease by 1/e is qc:

Example at: BC1: R=7.38m and cuoff=0.07 THz then c =65 mrad BC2: R=6.17m and cuoff=0.07 THz then c =69 mrad

Considering extraction of Thz radiation after 1m one gets:chamber width = at least 65-69mm !!

Note that average opening angle: q =1/BC1[E=0.22GeV] =2.33mrad------- BC2[E=0.6GeV] =0.85mrad

c=(3*c/R)1/3 where R is the bending radius.


Suitable window materials for Far infrared (and visible)

z-cut Quartz

Material Vacuum Environment Spectral Range

z-cut quartz: UHV 0.15 <l< 3.5mm 100mm<l<2mm

HDPE

(high density polyethylene)

HV 16mm <l< 2mm

TPX

(polymetylpentene)

HV 0.35 <l< 1.1mm

200mm <l< 2mm


Other diagnostics usable radiation sources:

CTR - Coherent Transition Radiation

destructivesimplehas useful intense optical emissionmature experience in diagnostics

CDR - Coherent Diffraction Radiation

non destructive !!weak optical emissionless mature but promising

Transition Radiation = lim (h->0) of Diffraction RadiationSame detection scheme for both CTR and CDR


TR and DR angular spectral distribution

References:Castellano et. al. PRST-AB 1 pg062801 (1998)Murokh et al. NIMPR-A 410 pg452 (1998)Rule et al. NIMPR-B 173 pg 67 (2001)

a slit of height “h” between infinite perfectly conducting semi-planes

•Transition radiation spectral distrib: approx. constant for >200nm

•DR less intense than TR in visible spectral region

•Coherent Enhancement factor is the same for both CTR and CDR.

R=h/(*X=xY=y


Diffraction Radiation Far field X,Y angular distributions

Transition radition

R=2

R=0.5R=0.5

R=2

R=h/(*

orthogonal polarization

parallel polarizationM.Veronese, M.Ferianis

CDR-CTR Targets design

Castellano group design for TTFVariable height rectangular slit at 45°

Very flexible but complex

OTR + fixed DR slits

TR-screen

e- beam

1 mm slit

2 mm slit

Less flexibleSimple extension ofTR- screen


EOS bunch arrival monitor diagnostics:

A non destructive shot-to-shot bunch arrival time in needed

It will be placed at the end of linac (E=1.2GeV)

Desired time resolution 100 fsec

Time window 10-20 ps

Our choice is EOS sampling based diagnostics


Spectral distribution function:

dI/d=k*|Ey()|2 where Ey()=F(Eyt(z))= F(Ey(z))*F((z)) with Ey

t(z)=Ey(z)*(z)

Typical Electric Field frequencies for FERMIless than 1 THz Phonon frequency of EO crystal (about 5.3THz ZnTe,11THz GaP)

40

e(x2+ y2 +2 z2)

xEx=

40

e(x2+ y2 +2 z2)

zEz=

40

e(x2+ y2 +2 z2)

zEy=

Transverse electric field of electron bunch

z

y

b

fs laser

EO crystal

e- bunch

Ex=0

40

e(b2 +2 z2)

zEz=

40

e(b2 +2 z2)

bEy=

on-axis

References:A.Cavalieri et al. PRL 94, 114801 (2005)S. Casalbuoni et al. TESLA Report 2005-01J.D.Jackson “Classical Elctrodynamics” M.Veronese, M.Ferianis

Estimated EOS signal

EOcrystal

/4pol. WollastonPrism

Balanced Detector

e-beam

EO Signal=|A1|2-|A2|2=sin()

where

= (d/0)n03r41Easqrt(1+3cos2())


Transverse Electric field intensity (Gaussian)

Medium Bunch Long Bunch


Bunch arrival EOS Layout

We need a single shot EO scheme ->, two main options:

BBO

EO

20ps

30fs

CCD

TEMPORAL DECODING

CCD

fs-laserEO

20ps

30fsSPATIAL DECODING

fs-laser

Spatial decoding (SPPS,VUV-FEL-proposed)

Temporal decoding(FELIX,TTF2):

Needs high power laserAppealing if seed laser branchcould be used

No need of high power laserPre-compensated fiber transmissionfrom MLO


Future work:CSR/CTR/CDR:

Transverse beam size,Low frequency cutoffs (vucuum chamber) simulations Impact of optics and detector on the signalComparison of available detectors (Diode, Golay cells, Pyroelectric)Feasibility of CDREvaluation of CTR EO autocorrelator for single shot measurementsEvaluation of single shot polychromator

EOS:Study effect of simulated bunch profile on EOSSimulation of THz and Laser propagation through the optics.Re-scaling of single shot scheme of SLAC to our case.

COTR: as bunching intra- undulator diagnostics has to be evaluated

Instrumentation:Choice of Laser for EO operation diags (800nm-30fsec): independent phase locked laser or MLO derived pulses.Set-up of laser test bench at Elettra including 800 nm, 30fs pulsed laser (Ti:Sa or Fiber Laser), FROG, GaAs THz wide area source,etc.


problem: determination of optimal compression of bc1 and bc2 and longitudinal feedback system....

Documents

ferianis slide

medium bunch long bunch

expected bunch

thz region

bc1 e bc2

exit bc1 medium

exit bc2 medium

linac end slide