Accelerator R&D at the Photo Injector Test facility at DESY in - PowerPoint PPT Presentation

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