Recent Experiments at PITZ 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 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 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 e.g. 800 µs ~ dB

Dark Current Study Maximum dark current vs. accelerating field Cs 2 Te Mo DC (Cs 2 Te) vs. I main and I buck

Old Laser System (until June 2003) UV 262 nm Pulse train up to 800  sec Repetition rate: 1 ~ 5 Hz Laser pulse length measurement with Streak camera FWHM = 7±1 psec Transverse laser profile Measured 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 ps rise/fall time ≈ 7 ps Trnasverse at virtual cathode  x = 0.47 ± 0.02 mm  y = 0.54 ± 0.02 mm

Phase Scan for Short Gaussian Laser (old system) Measurement ASTRA Simulation Gradient: ~40 MV/m Solenoid: 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 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 momentumRMS momentum spread Solenoid current = 280 A beam charge 1 nC (fixed) simulation measurement ASTRA simulation

radiator electron trajectory mirror vacuum tube vacuum window Streak camera 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)

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)

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 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