Recent Experiments at PITZ

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Recent Experiments at PITZ
Photo Injector Test Facility at DESY Zeuthen
J. H. Han for the PITZ collaboration
ICFA Future Light Sources Sub-Panel Mini Workshop
on Start-to-End Simulations of X-RAY FELs August
18-22, 2003 at DESY-Zeuthen, GERMANY
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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

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Goals

• Test facility for FELs TTF2-FEL, TESLA-XFEL,
  BESSY-FEL
• ? very small transverse emittance (1 ? mm mrad _at_
  1 nC)
• ? stable production of short bunches with small
  energy spread
• Extensive RD 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

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Current Layout
Collaboration
BESSY, Berlin DESY, Hamburg and Zeuthen INFN
Milano INR Troitsk INRNE Sofia Max-Born-Institute,
Berlin TU Darmstadt, department TEMF YERPHI
Yerevan
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RF Commissioning Results

• Max. rf pulse length 900 µs
• Max. repetition rate 10 Hz
• Max. accelerating field
• gt 40 MV/m at the cathode ( 3 MW)
• duty factor 0.9 ,
• average rf power 27 kW

Fulfills TTF2 rf parameter requirements
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Dark Current Study
Maximum dark current vs.accelerating field
DC (Cs2Te) vs. Imain and Ibuck
Cs2Te
Mo
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Old Laser System (until June 2003)
UV 262 nm Pulse train up to 800 ?sec Repetition
rate 1 5 Hz
Transverse laser profile Measured at virtual
cathode ?x0.50 0.02 mm ?y0.67 0.01 mm
Laser pulse length measurement with Streak
camera FWHM 71 psec
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New laser system Longitudinal Profiles
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Characteristic Laser Beam Profile
Trnasverse at virtual cathode ?x 0.47 0.02
mm ?y 0.54 0.02 mm
Longitudinal (Green) FWHM 24 ps rise/fall time
7 ps
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Phase Scan for Short Gaussian Laser(old system)

• Gradient 40 MV/m
• Solenoid max. at z 280 mm !
• max. Charge 0.5 nC
• Short and small laser beam
• High space charge force

Measurement
ASTRA Simulation
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Phase Scan with new Laser System
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
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Momentum Measurements as a Function of Phase
Mean momentum
RMS momentum spread
measurement ASTRA simulation
measurement
simulation
Solenoid current 280 A beam charge 1 nC (fixed)
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Bunch Length Measurement Setup

• Radiators
• Aerogel (BINP, n1.03)
• in a separate box
• Quartz
• OTR, metal plate tilted
• with 45 degrees

radiator
vacuum tube
electron trajectory
mirror
vacuum window
Streak camera
Optical transmission line about 26 m long
slit
Bandpass filter
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Bunch Length Measurement
Bunch length as a function of number of
micro-pulses (Aerogel) (10 measurements for one
point)
One example of the bunch length measurement

• 100 distributions taken for 1 bunch,
• standard deviation of mean time
• 1.0 ps (streak camera resolution 1.7 ps)

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Longitudinal Beam Distribution for 1 nC Bunch
90 RMS bunch length as a function of SP phase
Single distribution at phase with highest
momentum
Measurement ASTRA simulation
measurement
simulation
Bandpass filter used to prevent dispersion 12
nm bandwidth
-z, mm
(Smearing which can be done due to a resolution
is not applied in this simulation)
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Transverse Emittance
Scanning three beamlets at each measurement
condition
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Simulated Transverse Emittance for Transverse
Laser rms size of 0.50 mm (radial)
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Taking Laser Beam Profile for Simulation
50,000 macro-particles which satisfy the
actual laser beam profile were taken for
transverse longitudinal directions and combined
randomly
(Green)
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Comparison between Measurement and ASTRA
Simulation with Actual Laser Profile
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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 _at_ 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

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Thanks