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Recent Experiments at PITZ

Recent Experiments at PITZ. P hoto I njector T est Facility at DESY Z euthen. 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. Contents.

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Recent Experiments at PITZ

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  1. Recent Experiments at PITZ Photo Injector Test Facility at DESY Zeuthen J. H. Han for the PITZcollaboration 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

  2. 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

  3. 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

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

  5. ~ dB e.g. 800 µs 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

  6. Dark Current Study Maximum dark current vs.accelerating field DC (Cs2Te) vs. Imain and Ibuck Cs2Te Mo

  7. 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 x=0.50 ± 0.02 mm y=0.67 ± 0.01 mm Laser pulse length measurement with Streak camera FWHM = 7±1 psec

  8. New laser system: Longitudinal Profiles

  9. 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

  10. 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

  11. 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

  12. 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)

  13. Bunch Length Measurement Setup • Radiators: • Aerogel (BINP, n=1.03) • 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 Bandpass filter slit

  14. 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 resolution1.7 ps)

  15. Longitudinal Beam Distribution for 1 nC Bunch Single distribution at phase with highest momentum 90% RMS bunch length as a function of SP phase 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)

  16. Transverse Emittance Scanning three beamlets at each measurement condition

  17. Simulated Transverse Emittance for Transverse Laser rms size of 0.50 mm (radial)

  18. 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)

  19. Comparison between Measurement and ASTRA Simulation with Actual Laser Profile

  20. 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 800µs 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

  21. Thanks

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