Accelerator R&D at the Photo Injector Test facility at DESY in Zeuthen (PITZ) Frank Stephan for the PITZ Collaboration, Breckenridge, August 12 th -17 th , 2018 Content: • PITZ: collaboration, facility, operation parameters • Towards ultimate low emittance beams • Development of “green” photo cathodes • Next generation of pulsed RF gun • First considerations towards upgraded NC CW gun design • Applications: - Beam driven plasma acceleration: Self modulation of long particle beams o High transformer ratios in plasma o - Bunch microstructure generation with dielectric lined waveguides - High power, tunable THz source for pump-probe experiments at E-XFEL - First static UED measurements • Summary & Outlook
PITZ Collaboration Partners (formal contract signed) contract on green photocathodes Founding partners of PITZ: • INFN Milano (C.Pagani): photocathodes • DESY, HH & Z (leading institute) • INR Troitsk (L. Kravchuk): CDS, TDS, Gun5 • HZB (BESSY) (A. Jankowiak): magnets, vacuum • INRNE Sofia (D. Tonev, G. Asova): EMSY + personnel • MBI (S. Eisebitt): cathode laser • LAL Orsay (A. Stocchi): HEDA1 + HEDA2 • TU Darmstadt (TEMF, T. Weiland, H. DeGersem): simulations • STFC Daresbury (D. Angal-Kalinin, B.Militsyn): phase space tomography Other national partners: • Thailand Center of Excellence in Physics • Hamburg university : (T. Vilaithong, Ch. Thongbai): personnel - most PhD students; • YERPHI (V. Nikoghosyan) + CANDLE (V. Tsakanov, B. - HGF-Vernetzungsfond; Grigoryan), Yerevan : personnel - generation of short pulses - plasma experiments • HZDR : - BMBF-PC-laser-project between MBI, DESY and HZDR, until ~2009; - collaboration between HZB, HZDR, MBI and DESY in SC-gun-cluster International partners: • IAP Nizhny Novgorod + JINR Dubna : 3D elliptical laser pulses, THz radiation • INFN Frascati + Uni Roma II (L. Palumbo, M. Ferrario): TDS and E-meter pre-studies | Accelerator R&D at PITZ | Frank Stephan for the PITZ Collaboration | 18 th AAC Workshop | Breckenridge, August 12 th -17 th , 2018 Page 2
Photo Injector Test facility at DESY, Zeuthen site (PITZ) Development, test and optimization of high brightness electron sources for SC linac driven FELs + applications: • test-bed for FEL injectors, e.g. FLASH and European XFEL ( gun cavities and photo injector subsystems e.g. lasers ) high brightness small e tr (projected and slice), lots of beam diagnostics • • further studies e.g. cathodes : dark current, photoemission, QE, thermal emittance , … applications like plasma acceleration , THz , UED , … <7 MeV <25 MeV booster Pulse Train Time Structure : RF gun PITZ and EXFEL run bunch trains with up to 600 ( 2700 ) laser pulses • L-band (1.3 GHz) 1.6-cell copper cavity flexible shapes 600 s • Ecath >~60MV/m 7MeV/c e-beams t • 650us x 10Hz up to 45 kW av. RF power • Cs 2 Te PC (QE~5-10%) up to 5nC/bunch 100 ms • LLRF control for amp & phase stability • Solenoids for emittance compensation t t = 1 s (222ns) | Accelerator R&D at PITZ | Frank Stephan for the PITZ Collaboration | 18th AAC Workshop | Breckenridge, August 12th-17th, 2018 Page 3
Towards ultimate low emittance beams 3D ellipsoidal pulses Simulated slice emittance (1nC) 1,2 60 still WR on lowest emittance slice emittance (mm mrad) (Gaussian) measured projected 1 50 emittances 0,8 40 emittance current (A) M. Krasilnikov et al., PRST-AB 15, (flattop) 100701 (2012) 0,6 30 emittance 0,4 20 (3D- ellipsoidal) 0,2 10 current (flattop) 0 0 z-<z> (mm) -5 -4 -3 -2 -1 0 1 2 3 4 5 6 • Laser shaping key for optimizing photoinjector brightness . • Ellipsoidal laser shaping benefits high bunch charge beams or CW guns (lower gun gradients). Two methods to generate 3D ellipsoidal photo cathode laser pulses are under study: • Mironov et al., Appl. Opt . 55 , p. 1630 (2016) • Mironov et al., Laser Phys. Lett. 13 , p. 055003 (2016) | Accelerator R&D at PITZ | Frank Stephan for the PITZ Collaboration | 18th AAC Workshop | Breckenridge, August 12th-17th, 2018 Page 4
Developing 3D ellipsoidal laser pulses First experimental results IR Spectrogram Proof of principle demonstrated with IAP system Pharos laser (single SLM dual path) at PITZ in 2016 Spectrograph Comparison with simulated e - beam shapes (500pC): similarity in shape Inverted MZ Interferometer 20 SLM Gaussian laser Ellipsoidal laser SLM Flattop laser 10 t (ps) 0 -10 @ EMSY1 @PST.Scr1 -20 -10 -5 0 5 10 x (mm) SLM capabilities at First Measurement J. Good et al., Proc. 38 th FEL Conf., WEP006 (2017) proper transport Redesign to true double SLM setup based on commercial Pharos laser • Improved stability: Polaris mounting system, new amplifier scheme with commercial Pharos: 200 µJ, 0.1 MHz with 245 fs pulse duration @ 1030 nm • Improved shaping capabilities: independent masking in x-y, spectrograph feedback • Next: - experiments to quantify shape preserving FHG conversion with angular chirp - true 3D shaping with Volume Bragg Gratings Simulation C. Koschitzki et al., Proc. 9 th IPAC, WEPMF059 (2018) | Accelerator R&D at PITZ | Frank Stephan for the PITZ Collaboration | 18th AAC Workshop | Breckenridge, August 12th-17th, 2018 Page 5
Development of green cathodes on INFN LASA plug design The INFN LASA Milano plug design is in operation at PITZ / XFEL / FLASH / REGAE / SINBAD / LBNL / FNAL. The aim of this activity is to grow reliable “ green ” cathodes (K -Cs-Sb compound) on the INFN plugs and test them in the PITZ RF-Gun (high cathode gradient + fairly high duty cycle) • First sequential deposition on test sample in week 47/2017 (“proof of principle”) - Sb 10 nm View into - K until max QE the prep chamber - Cs until max QE - Repeated on 1 Dec 2017 • Long term measurement - Total extracted charge over more than 3 months (full light spectrum) Total Extracted Charge Total Extracted Charge - QE versus time QE versus time QE versus time 2000 2000 1.2 1.2 Laser Driven Light Source broad band LED • Based system pressure 1800 1800 1 power density ( ~21𝑛𝑋/𝑑𝑛² ) power density ( 8 𝑛𝑋/𝑑𝑛² ) LED LED LDLS LDLS 1.0 1.0 1600 1600 Extracted charge [C] Extracted charge [C] in the low 10 -10 mbar 1400 1400 0.8 0.8 1200 1200 QE [a.u.] QE [a.u.] • QE decrease depends on 1000 1000 0.6 0.6 light power density (fatigue effect?) 800 800 0.4 0.4 No light No light 600 600 still reasonable QE 400 400 No light 0.2 0.2 200 200 • Next: Design new source layout in view 0.0 0.0 0 0 0 0 480 480 960 960 1440 1440 1920 1920 2400 2400 2880 2880 3360 3360 0 0 480 480 960 960 1440 1440 1920 1920 2400 2400 2880 2880 3360 3360 Time [hours] Time [hours] of co-evaporation in the near future Time [hours] Time [hours] | Accelerator R&D at PITZ | Frank Stephan for the PITZ Collaboration | 18th AAC Workshop | Breckenridge, August 12th-17th, 2018 Page 6
Next generation of pulsed RF gun under production Fabrication of Gun 5 for higher stability & reliability has started New features of Gun 5 ( see V. Paramonov et al., NIM A 854 (2017) 113-126. ): • includes RF probe + fine control of RF stability + allows symmetric power coupler (2 input arms reduced load on RF windows) - possible sensitivity on pulsed heating experimental tests needed • increased water cooling and reduced deformation over RF pulse more reliable operation at high duty cycle • improved cell geometry + elliptical irises reduced RF heating & surface field strength Cavity RF pickup First (central) part under production now | Accelerator R&D at PITZ | Frank Stephan for the PITZ Collaboration | 18th AAC Workshop | Breckenridge, August 12th-17th, 2018 Page 7
First considerations towards upgraded NC CW gun design Backup design for European XFEL CW upgrade Preliminary design of DESY VHF gun (217 MHz) CW gun design collaboration DESY 217MHz • DESY group visit to LBNL and SLAC (2/2018). • Collaboration with LBNL on NC CW gun development. PITZ design progress ( still preliminary !!! ) APEX 187MHz • Design tool benchmarked using APEX gun model (187 MHz). • RF design of a 217 MHz gun for European XFEL Preliminary injector simulation with DESY VHF gun (100 pC) started this year, targeting ~30 MV/m at cathode, ~100 kW RF power. • Current gun design plugged into LCLS-II injector model shows emittance ( 0.10~0.16 μ m ) and high order energy spread ( 3~4 keV rms ) @ 100 pC with I peak =10A. • Gun geometry, injector layout and optics are still under further optimizations. | Accelerator R&D at PITZ | Frank Stephan for the PITZ Collaboration | 18th AAC Workshop | Breckenridge, August 12th-17th, 2018 Page 8
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