High Rep Rate Guns: FZD Superconducting RF Photogun J. Teichert, A. Arnold, H. Büttig, D. Janssen, M. Justus, U. Lehnert, P. Michel, K. Moeller, P. Murcek, Ch. Schneider, R. Schurig, G. Staats, F. Staufenbiel, H. Tietze, R. Xiang, P. Kneisel, B. v. d. Horst, A. Matheisen, J. Stephan T. Kamps, J. Rudolph, M. Schenk, G. Klemz, I. Will, V. Volkov FLS 2010 Workshop, SLAC, March, 1-5, 2010
INTRODUCTION HISTORY OF SRF GUN R&D 1988-91 proposal & first experiment A. Michalke, PhD Thesis, WUB-DIS 92-5 Univ. Wuppertal, 1992 1 2 3 4 2002 first beam from a SCRF gun @ FZD D. Janssen et al., NIM-A, Vol. 507(2003)314 8 7 6 5 since 2004: Development of the 3½-Cell SRF Photoinjector for ELBE A. Arnold et al., NIM-A, Vol. 577(2006)440
COMMISSIONING FIRST COOL-DOWN first cool-down 1 2 August 2007 1,3005G 1,3000G frequency [Hz] 1,2995G f=2.02mhz 1,2990G 1,2985G 1,2980G temperature [K] 0 50 100 150 200 250 300
COMMISSIONING - FIRST ELECTRON BEAM first beam of the 3½ cell SRF gun on November 12 th, 2007 RF: E acc = 5 MV/m f = 1300. 38327 MHz, 150 Hz bandwidth P diss = 6 W Laser: 263 nm, 100 khz reprate 0.4 W power (4 µj) Cu cathode Cathode: Cu, Q.E. 10-6 Electron beam: 2.0 MV energy 50 na average current,0.5 pc bunch charge
INTRODUCTION ELBE Superconducting RF Photoinjector New Injector for the ELBE SC Linac Test Bench for SRF Gun R&D Mode ELBE High Charge final electron energy RF frequency operation mode 9.5 MeV 1.3 GHz CW bunch charge 77 pc 1 nc repetition rate 13 MHz 500 khz laser pulse (FWHM) 4 ps 15 ps transverse rms emittance 1 mm mrad 2.5 mm mrad average current 1 ma 0.5 ma
Design for the SRF-Gun @ ELBE CW + high rep rate - 500 khz, 13 MHz and higher medium average current 1 2 ma (< 10 ma) high energy (stand alone) - 3½ cells low - high bunch charge 80pC 1 nc low transverse emittance 1 3 mm mrad normal-conducting, lqn 2 -cooled, exchangeable, semi-conductor photo cathode highly compatible with ELBE cryomodule (1.3 GHz cavity, 10 kw coupler, He & N2 support, etc.) Application @ ELBE high peak-current operation for FELs with (13 MHz, 80 pc) high current (1 ma) @ low rep rate (<1 MHz) -> high charge pulsed secondary particle beams: neutrons, positrons with ToF measurements low emittance @ medium charge (100 pc) for short pulses THz-radiation x-rays by inverse Compton backscattering
MAIN COMPONENTS helium port cavity tuners Liquid He Vessel SRF Gun Cryomodule photo cathode alignment LASER e - cathode cooling (77 K) & support system rf power coupler SC Nb 3½ -cell cavity NC Cs 2 Te photo cathode
MEASUREMENT & OPERATION PARAMETERS SRF Gun Parameter parameter present cavity new high gradient cavity measured 08 ELBE high charge ELBE high charge final electron energy 2.1 MeV 3 MeV 9.5 MeV peak field 13.5 MV/m 18 MV/m 50 MV/m laser rep. rate 1 125 khz 13 MHz 2 250 khz 13 MHz 500 khz laser pulse length (FWHM) 15 ps 4 ps 15 ps 4 ps 15 ps laser spot size 2.7 mm 5.2 mm 5.2 mm 2 mm 5 mm bunch charge 200 pc 77 pc 400 pc 77 pc 1 nc max. aver. Current 1 µa 1 ma 100 µa 1 ma 0.5 ma peak current 13 A 20 A 26 A 20 A 67 A transverse. norm. emittance (rms) 3 1 mm mrad @ 80 pc 2 mm mrad 7.5 mm mrad 1 mm mrad 2.5 mm mrad
3½ CELL CAVITY Treatment and test of the cavity 1E10 achieved peak axis fields of all 4 vertical test benches Tests in the vertical cryostat (1.8 K) at DESY in 2007 Q 0 1E9 all 4 tests limited by field emission V-Test 1 V-Test 2 V-Test 3 V-Test 4 0.0 10.0M 20.0M 30.0M 40.0M 50.0M E peak in V/m HPR cleaning very difficult, surface damaged after 4 vertical test at DESY improvement not expected cavity used as it was, assembly continued
3½ CELL CAVITY Cavity performance in the gun Helium consumption measurement E E peak acc = 2.7 maximum achievable field only 1/3 of the designed value of E peak =50 MV/m, measured Q 0 is 10 times lower than in all vertical tests, gradient is limited by field emission no Q degradation found since the 1 st measurement in 2007, Improvement by (9th test) high power processing (HPP) results 3 MeV operation After warming-up or cathode exchange the HPP must be repeated
3½ CELL CAVITY Energy and energy spread @ 5 pc (w/o space charge)
3½ CELL CAVITY He pressure effect on cavity frequency 31,5 SRF Gun: ~ 230 Hz / 1mbar ELBE Linac: ~ 35Hz / 1mbar 31,2 RF MEASUREMENTS pressure [mbar] f 0 [Hz] 1,30038132G 1,30038126G 1,30038120G 1300381200 1300381180 1300381160 1300381140 Messwerte f 0 vs. P lineare Regression 30,9 1,30038114G 1,30038108G 30,6 1,30038102G 09:36 10:48 12:00 13:12 14:24 15:36 time [hh:mm] 1300381120 f 1300381100 0 [Hz] 1300381080 1300381060 1300381040 =232,61337 Hz/mBar 1300381020 P [mbar] 1300381000 30,6 30,7 30,8 30,9 31,0 31,1 31,2 31,3 SRF-gun ~230 Hz/mbar ELBE module ~35 Hz/mbar Lorentz force detuning SRF-gun K= 0.69 Hz/(MV/m)² ELBE module K = 0.25 Hz/(MV/m)² (with respect to peak fields)
3½ CELL CAVITY New High Gradient Cavity old design new design Improvements higher stiffness of the half-cell back wall microphonics, Lorentz force detuning larger opening in choke and partly in half-cell better HPR cleaning new pick-up antenna design, etc. simpler clean-room assembly
3½ CELL CAVITY New High Gradient Cavity Fabricated in collaboration with JLab, thanks to P. Kneisel now: warm tuning @ JLab next: warm rf measurements @ FZD cleaning & test @ JLab standard RRR 300 Nb cavity Large grain Nb cavity
Cs 2 Te PHOTO CATHODES Photo Cathode Transfer System Photo cathode preparation equipment at FZD bayonet fixing pressure spring cone for positioning & thermal contact Ø10 mm Cs 2 Te
Cs 2 Te PHOTO CATHODES Photo Cathode Transfer System Lock Places for 6 cathodes Transport chamber Transfer chamber Cool PC exchange works Change of PC needs ~30 min Docking of transport chamber needs 1 maintenance shift + 1 week backing (during ELBE operation) Cathode transfer rod linear & rotation Use of semiconductor photo cathodes like Cs 2 Te requires a UHV exchange system with <10 9 mbar
UV LASER SYSTEM UV CW Laser system delivered by MBI Laser upgrade 2010 (0.5 W @ 262 nm) Two oscillators 13 MHz: Nd:glass oscillator (26 mhz) 3 ps FWHM Gaussian 500, 250, 125 khz: Nd:YLF oscillator (26 mhz) 14 ps FWHM Gaussian one amplifier Nd:YLF multipass amplifier 10-20 W existing 250 khz laser with Nd:YLF regenerative amplifier two UV converters two-stage frequency converters (LBO, BBO)
UV LASER SYSTEM Upgrade of the laser beam line & virtual cathode remote-controlled laser spot size setting (telescope & aperture) Measurement of laser profile, position, and power on the virtual cathode screen
BEAM PARAMETER MEASUREMENT - DIAGNOSTICS BEAMLINE diagnostics beamline designed and built by HZB (BESSY) Berlin - Laser input port, Solenoid - Current & Charge (Faraday-cup & ICTs) - Transverse Emittance (slit mask, solenoid scan) - Energy and E (C-bent) - Bunch length (Cherenkov radiator with optical beamline and streak camera, electro-optical sampling
ELBE INJECTION Installation of electron beamline to ELBE was finished in winter shutdown 2009/10 First accelerated SRF gun beam at ELBE on Febr. 5, 2010
ELBE INJECTION 5 MeV energy increase Compared to thermionic injector 3 MeV from SRF gun, 2 MeV from on-crest injection
SUMMARY In 2009 Upgrade of the cathode transfer system: sufficient vacuum, backing during ELBE operation Installation of the beam line to ELBE Commissioning of the Cherenkov station for bunch length measurements Spectrometer for slice emittance measurements delivered Design upgrade and fabrication of two new high gradient cavities Outstanding and planned for 2010 Demonstration of ELBE injection Preparation and Test of the new cavities at JLab Demonstration of high-current operation with 13 MHz laser & PC >1% QE Systematic experimental studies of HOM excitation in the gun Measurements & Optimization to find the bunch charge limit at 3 MeV First ELBE user beam with SRF gun
THANK YOU FOR YOUR ATTENTION Thanks to the ELBE crew, the technical staff of BESSY, DESY and MBI, to RI, JLab, and all the others supported and encouraged this project Acknowledgement We acknowledge the support of the European Community-Research Infrastructure Activity under the FP6 programme 2004-08 (CARE, contract number RII3-CT-2003-506395) and the FP7 programme since 2009 (EuCARD, contract number 227579) as well as the support of the German Federal Ministry of Education and Research grant 05 ES4BR1/8.