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Cathode Laser Pulse Shaping For High Brightness Electron Sources (PITZ Experience)

Cathode Laser Pulse Shaping For High Brightness Electron Sources (PITZ Experience). Mikhail Krasilnikov (DESY) for the PITZ Team. ICFA Workshop on Future Light Sources, March 5-9, 2012 Thomas Jefferson National Accelerator Facility, Newport News, VA. Content:

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Cathode Laser Pulse Shaping For High Brightness Electron Sources (PITZ Experience)

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  1. Cathode Laser Pulse Shaping For High Brightness Electron Sources(PITZ Experience) Mikhail Krasilnikov (DESY) for the PITZ Team ICFA Workshop on Future Light Sources, March 5-9, 2012Thomas Jefferson National Accelerator Facility, Newport News, VA • Content: • Photo cathode laser system at PITZ • Temporal pulse shaping – flat-top profile: • rise/fall time impact • flat-top modulations studies • Transverse laser distribution influence • Advanced pulse shaping of the cathode laser: 3D ellipsoid • Summary

  2. Yb:YAG laser at PITZ with integrated optical sampling system PITZ Photo cathode laser (Max-Born-Institute, Berlin) t ~ 1.7 ps Highly-stable Yb:YAG oscillator pulse selector Optical Sampling System (OSS) Emicro= 0.002 mJ Nonlinear fiber amplifier Emicro= 0.002 mJ pulse shaper Resolution: t < 0.5…1 ps scanning amplifier(Yb:KGW) Yb:YAG power regenG ~ 106 Emicro~ 2 mJ UV output pulses Emicro~ 10 mJ Pulse selector Two-stage Yb:YAG double-pass amplifierG ~ 40 LBO BBO Emicro~ 80 mJ

  3. OSS signal (UV) FWHM = 25 ps edge10-90~ 2ps edge10-90~ 2.2 ps birefringent shaper, 13 crystals Multicrystal birefringent pulse shaper containing 13 crystals Photo cathode laser: temporal pulse shaping temperature controlled birefringent crystal motorized rotationstage Shaped ouputpulses Gaussianinputpulses Will, Klemz, Optics Express 16 (2008) , 4922-14935

  4. Photo cathode laser: flat-top temporal pulse profiles Laser temporal profile used for the emittance optimization at various bunch charge levels

  5. Check effect on rise/fall time – results of 2009 Best measurements (22.08.2009M) • Q=1nC • Imainoptimized • Gun: +6deg off-crest • Booster: on-crest • Laser: temp FWHM~20ps, BSA=1.5mm • In 2009 it was not possible to measure the effect with current machine stability • After the improvement of the phase stability the effect is planned to be rechecked (this year)

  6. Various laser temporal flat-top modulationsSimulations 2 peaks simulations with gun on-crest, other parameters optimized 3 peaks 4 peaks 5 peaks • higher modulation frequency  larger emittance growth rate • reliable simulations for modulations with >5 peaks are difficult

  7. Laser temporal profile modulationsExperiment: measurements in 2009 default 2 peaks 3 peaks 4 peaks In 2009 it was not possible to measure the effect with the current machine stability

  8. Measurements with / without modulations on the temporal laser distribution Approach  detuning of an aligned pulse shaper, i.e. by purpose introducing modulations on the flat-top of the temporal laser distribution and measuring momentum distribution in HEDA Machine conditions: • gun: on-crest • booster: +10deg off-crest • bunch charge: 500pC Laser temporal profiles without modulations with modulations Electron beam longitudinal momentum distribution Electron beam longitudinal momentum distribution (5 laser pulses used) (1 laser pulse used)

  9. Resonantlydrivenplasmawave  high tranformationratio  5 Bunchletsinsidethebunch: Studies for Particle Driven Plasma Acceleration @PITZ • Self-modulation withseed pulse: Output parameters for 2 sub-bunches @6.28m from cathode: Gauss: V Flat-top: • Self-modulation withoutseed but with flat-top modulation: Photo cathode laser distributions probe bunch tobesenttobunchcompres-sor V

  10. Photo cathode laser: transverse pulse shaping laser spot at “virtual cathode” laser beam steering imaging of the BSA onto the photo cathode Beam Shaping Aperture (BSA) plate is now replaced by an iris with remotely tunable opening

  11. Photo cathode laser: transverse distributions BSA=1.2mm (1nC) BSA=0.5mm (0.1nC) RMS sizes (no Gaussian fit!) sx=0.13 mm and sy=0.12 mm RMS sizes (no Gaussian fit!) sx=0.30 mm and sy=0.29 mm

  12. “Fresh Cathode Effect” studies 07.05.2011 • 07.05.2011M – “Old” cathode (#110.2)  best 1nC machine setup (+cathode measurements: dark current, QE maps) • 07.05.2011N – “New” (fresh) cathode (#11.3)  best 1nC machine setup (+cathode measurements : dark current, QE maps) Old cathode #110.2 QE-map New cathode #11.3 QE-map Cathode laser Cathode laser e-beam at EMSY1 e-beam at EMSY1 07.05.2011M 3x3 stat: X-emit=0.742±0.021 Y-emit=0.782±0.028 XY-emit=0.761±0.022 07.05.2011N: 3x3 stat: Xemit=0.724±0.056 Y-emit=0.603±0.038 XY-emit=0.661±0.046

  13. Laser pulse shaping studies for further improvement of the electron beam quality in a photo injector 3D ellipsoidal cylindrical temporally Gaussian (e.g. FLASH) Trms=4.4ps Flat-top (e.g PITZ) FWHM~20ps, rt~2ps Beam dynamics (ASTRA) simulations for PITZ-1.8 setup

  14. Core emittance BD simulations for bunch charge 1 nC Slice parameters at z=5.74m

  15. BD simulations for bunch charge 1 nC Transverse phase space at z=5.74m Electron beam transverse distribution at z=5.74m almost no beam halo reduced beam halo

  16. BD simulations for bunch charge 1 nC Electron beam (Z-X) shape at z=5.74m Longitudinal phase space (Z-Pz) at z=5.74m less nonlinearity

  17. Conclusions • Cathode laser pulse shaping is one of the key parameters for a high brightness photo injector • Nominal temporal pulse shape at PITZ – a flat-top of ~ 20ps FWHM • Short rise/fall time, first trials were performed in 2009, to be checked soon • Flat-top modulations: no large impact onto the transverse phase space, but longitudinal phase space modulations • Transverse laser distribution: • Laser transport and imaging to the cathode • “Fresh cathode” effect  homogeneous emission area • Beam dynamics simulations applying a 3D pulse shaping (ellipsoid) for the PITZ injector yield : • significant reduction in beam projected and slice emittance • reduced beam halo and less sensitivity to machine parameters • less nonlinear longitudinal phase space practical realization  BMBF project with IAP, Nizhniy Novgorod, Russia

  18. The End

  19. Core emittance BD simulations for bunch charge 100 pC Slice parameters at z=5.74m

  20. BD simulations for bunch charge 100 pC Transverse phase space at z=5.74m almost no beam halo

  21. BD simulations for bunch charge 100 pC Electron beam (Z-X) shape at z=5.74m Longitudinal phase space (Z-Pz) at z=5.74m

  22. BD simulations for bunch charge 1 nC Tolerances In the case of the ellipsoidal shaping the electron beam quality is less sensitive to machine parameters (e.g. main solenoid peak field)

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