Recent Experiments at PITZ
ICFA Future Light Sources Sub-Panel Mini Workshop on Start-to-End Simulations of X-RAY FELsAugust 18-22, 2003 at DESY-Zeuthen, GERMANY
J. H. Han
for the PITZ collaboration
Photo Injector Test Facility at DESY Zeuthen
Contents
• Goal of PITZ, Experimental setup• RF results:
– RF conditioning– Dark current
• Photocathode Laser• Beam measurements:
– Phase scan (beam charge measurement)– Beam momentum measurement– Bunch length measurement– Transverse emittance measurement
• Summary and Outlook
Goals
• Test facility for FELs: TTF2-FEL, TESLA-XFEL, BESSY-FEL
very small transverse emittance (1 mm mrad @ 1 nC)
stable production of short bunches with small energy spread
• Extensive R&D on photoinjectors in parallel to TTF operation
• Comparing detailed experimental results with simulations:
benchmark theoretical understanding of photoinjectors
• Test and optimization of rf gun cavities for subsequent operation at TTF2-FEL and TESLA-XFEL
• Test of new developments (laser, cathodes, beam diagnostics)
• In future for TESLA: flat beams, polarized electrons
Current goal: full characterization of the photoinjector rf gun
BESSY, Berlin
DESY, Hamburg and Zeuthen
INFN Milano
INR Troitsk
INRNE Sofia
Max-Born-Institute, Berlin
TU Darmstadt, department TEMF
YERPHI Yerevan
Current LayoutCollaboration:
RF Commissioning Results
- Max. rf pulse length: 900 µs
- Max. repetition rate: 10 Hz
- Max. accelerating field:
> 40 MV/m at the cathode (~ 3 MW) duty factor: 0.9 %,
average rf power: 27 kW
Fulfills TTF2 rf parameter requirements
0.2
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800 1000 1200 1400 1600 1800 2000 2200
t / sec
a.u. Forw ard pow er
R eflected pow er
e.g. 800 µs
~ dB
Dark Current Study
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33 34 35 36 37 38 39 40 41 42E lec tric fie ld a t th e ca thode (M V /m )
Da
rkcu
rren
t(uA
)
Maximum dark current vs.
accelerating field
Cs2Te
Mo
DC (Cs2Te) vs. Imain and Ibuck
Old Laser System (until June 2003)UV 262 nmPulse train up to 800 secRepetition rate: 1 ~ 5 Hz
Laser pulse length measurementwith Streak cameraFWHM = 7±1 psec
Transverse laser profileMeasured at virtual cathode
x=0.50 ± 0.02 mm
y=0.67 ± 0.01 mm
New laser system: Longitudinal Profiles
Characteristic Laser Beam Profile
Longitudinal (Green)FWHM ≈ 24 psrise/fall time ≈ 7 ps
Trnasverse at virtual cathodex = 0.47 ± 0.02 mmy = 0.54 ± 0.02 mm
Phase Scan for Short Gaussian Laser(old system)
Measurement
ASTRA Simulation
Gradient: ~40 MV/mSolenoid: max. at z = 280 mm !max. Charge ~ 0.5 nC Short and small laser beam High space charge force
Phase Scan with new Laser System
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020406080100120140160180
I mai
n /
A
Phase / deg
Beam Charge / nC
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Gradient: ~40 MV/m
Solenoid:max. at z = 280mm
max. Charge ~ 1.6 nC
Laser parameters have a significant influence on charge production
Simulations ongoing
Momentum Measurements as a Function of Phase
Mean momentum RMS momentum spread
Solenoid current = 280 Abeam charge 1 nC (fixed)
simulation
measurementmeasurement
ASTRA simulation
radiatorelectrontrajectory
mirror
vacuumtube
vacuum window
Streakcamera
slit
Optical transmission line about 26 m long
Radiators:- Aerogel (BINP, n=1.03) in a separate box- Quartz- OTR, metal plate tilted with 45 degrees
Bandpass filter
Bunch Length Measurement Setup
Bunch length as a function of number of micro-pulses (Aerogel):
(10 measurements for one point)
100 distributions taken for 1 bunch, standard deviation of mean time
= 1.0 ps (streak camera resolution 1.7 ps)
Bunch Length Measurement
One example of the bunch length measurement
-z, mm
simulation
measurement
90% RMS bunch length as a function of SP phase
Single distribution at phase with highest momentum
(Smearing which can be done due to a resolution is not applied in this simulation)
Bandpass filter used to prevent dispersion: 12 nm bandwidth
Measurement
ASTRA simulation
Longitudinal Beam Distribution for 1 nC Bunch
Transverse Emittance
Scanning three beamlets at each measurement condition
Simulated Transverse Emittance for Transverse Laser rms size of 0.50 mm (radial)
1nC; 23 ps FWHM, emittance X
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290 295 300 305 310 315
I_main (A)
pi m
m m
rad
-10deg X
-5deg X
0deg X
+5deg X
+10deg X
1nC; 23ps FWHM, emittance Y
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4,0
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I_main (A)
pi m
m m
rad
-10deg Y
-5deg Y
0deg Y
+5deg Y
+10deg Y
Taking Laser Beam Profile for Simulation
50,000 macro-particles which satisfy the actuallaser beam profilewere taken for transverse& longitudinal directionsand combined randomly
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(Green)
X Emittance
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0 degree
-5 degree
Y Emittance
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0 degree
-5 degree
Comparison between Measurement and ASTRA Simulation with Actual Laser Profile
Summary / Outlook
• PITZ has been brought into operation within an international collaboration
• RF specifications for TTF2 have been reached
• Laser system with longitudinal pulse shaping for pulse trains up to 800 µs is in operation
• Characterization of electron source is ongoing:
Mean momentum (~ 4.7 MeV/c) & momentum spread
(~ 30 keV/c)
Bunch length (~ 2.5 mm rms)
Transverse Emittance (3 mm mrad @ 1 nC)
are measured
• Cavity will be installed at TTF2 in autumn 2003
• Upgrade of the facility (e.g. booster cavity) is foreseen, further collaboration is welcome
Thanks
