1. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE J. Teichert, A. Arnold, H. Büttig, D. Janssen, M. Justus, U. Lehnert, P. Michel, P. Murcek, A. Schamlott, C. Schneider, R. Schurig, F. Staufenbiel, R. Xiang, T. Kamps, J. Rudolph, M. Schenk, G. Klemz, I. Will for the BESSY-DESY-FZD-MBI collaboration The Superconducting RF Photoinjector at ELBE – First Operational Experience Workshop on Sources of Polarized Electrons and High Brightness Electron Beams October 1-3, 2008, Jefferson Lab, Newport News, VA

2. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE INTRODUCTION – MOTIVATION FOR SRF GUN Int. FEL Community Radiation Source ELBE High Brightness High Average Current CW Operation Low RF Power Dissipation 250 kV thermionic Gun CW operation but low brightness low bunch charge NC RF photogun highest brightness but low average current high current gun for 4th generation light sources ? NEW CHALLANGES SC Cavity Design with Cathode Insert Cavity Degradation during Operation Choice of Photo cathode type Coupling RF power in cavity & HOM effects emittance growth compensation method

3. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE INTRODUCTION – HISTORY OF SRF GUN R&D 1988-91 proposal & first experiment A. Michalke, PhD Thesis, WUB-DIS 92-5 Univ. Wuppertal, 1992 since 2004 ELBE SRF Photoinjector A. Arnold et al., NIM-A, Vol. 577(2006)440 2002 first beam from a SRF gun D. Janssen et al., NIM-A, Vol. 507(2003)314

4. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE INTRODUCTION ELBE Superconducting RF Photoinjector New Injector for the ELBE SC Linac Test Bench for SRF Gun R&D ModeELBEHigh Charge final electron energy≤ 9.5 MeV RF frequency1.3 GHz operation modeCW bunch charge77 pC1 nC repetition rate13 MHz500 kHz laser pulse (FWHM)4 ps15 ps transverse rms emittance 1 mm mrad 2.5 mm mrad average current1 mA0.5 mA

5. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE LASER NC Cs 2 Te photo cathode helium port SC Nb 3½ -cell cavity e-e- MAIN COMPONENTS Liquid He Vessel cathode cooling (77 K) & support system photo cathode alignment cavity tuners rf power coupler SRF Gun Cryomodule

6. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE DESIGN & PARAMETERS Niobium Cavity Nb RRR 300 cavity –design values E acc = 25 MV/m in TESLA cells, Q 0 =1x10 10 110 mT maximum magnetic surface field E peak (TESLA cells) = 50 MV/m E peak (half-cell) = 30 MV/m E cathode = 20 MV/m (retracted cathode) MAIN COMPONENTS Results of the 4 vertical tests at DESY HPR cleaning very difficult demage produced use of the cavity, since further improvement not expected

7. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE COMMISSIONING – FIRST COOL-DOWN first cool-down 1 – 2 August 2007

8. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE Quality factor and Gradient measurements E acc E peak E acc (TESLA)E electron 5.5 MV/m15.5 MV/m8 MV/m2.5 MV He consumption measurement and calibrated pick-up constant He flow change of electrical heater power COMMISSIONING – RF TESTS

9. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE RF MEASUREMENTS Measurement of RF properties: COMMISSIONING – RF TESTS On-Axis Field distribution He Pressure Sensitivity Lorentz Force Detuning Microphonics Higher-Order Mode Excitation Tuning System Performance long term behavior of Q 0 vs. E acc curve for details see André Arnolds Poster

10. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE COMMISSIONING – RF TESTS High-Power Processing of Cavity Processing with pulsed RF for reduction of field emission in Sept. 08 High risk process – at the end of the measurement period Improvement of acceleration gradient Eacc = 5 -> 6.5 MV/m Gun Operation with E e = 3 MeV in next run (instead of 2 MeV before)

11. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE COMMISSIONING – UV LASER INSTALLATION Laser pulse lateral: shaped with aperture to Ø 2.7 mm circular flat top 500 kHz Laser system developed by MBI 262 nm CW laser mit 0.5 W /UV) Nd:YLF oscillator Nd:YLF regenerative amplifier two-stage frequ. conv. (LBO, BBO) 15 ps FWHM Gaussian

12. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE ELBE shut-down, Oct. 15 – 26, 2007 Installation of BESSY diagnostics beamline - Emittance measurement (slit mask) - C bend (E,  E) - Cherenkov radiatior with optical beamline and streak camera COMMISIONING - DIAGNOSTICS BEAMLINE

13. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE FIRST ELECTRON BEAM Cu cathode First beam of the 3½ cell superconducting rf photo gun on November 12th, 2007 Beam spot on the first YAG screen in the BESSY diagnostics beamline 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) temporal profile: 15 ps FWHM Gaussian lateral profile: 4 mm x 6mm spot, Gaussian Cathode: Cu, Q.E. ≈ 10 -6 Electron beam: 2.0 MV energy 50 nA average current,0.5 pC bunch charge

14. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE COMMISIONING - CATHODE TRANFER SYSTEM INSTALLATION Transfer chamber Transport chamber Lock Cathode transfer rod linear & rotation Places for 6 cathodes installation in the shut-downs of ELBE in Jan. + March 08 at the SRF gun

15. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE Cs 2 Te PHOTO CATHODES Photo cathode preparation lab at FZD preparation processstorage & recovery May 08: First set of Cs 2 Te cathodes in the SRF gun QE scan in SRF gun QE = 10 -3 bad“ vacuum in transfer chamber and during manupulation

16. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE BEAM PARAMETER MEASUREMENT Schottky scan – optimum laser phase screen DV02 (YAG) 1.9 m from gun exit, 2.7 m from cathode -175°, σ x = 300 µm -150°, σ x = 330 µm -130°, σ x = 610 µm -115°, σ x = 760 µm -95°, σ x = 330 µm -65°, σ x = 430 µm +3°, σ x = 1650 µm

17. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE BEAM PARAMETER MEASUREMENT Schottky scan – laser phase variation @ constant laser power Laser temporal profile: 15 ps FWHM Gaussian spacial profile: 2.7 mm spot diameter flat top Faraday cup 0.6 m from gun exit, 1.4 m from cathode space charge smoothing Φ laser = 0° slope determined by laser pulse length Laser pulse rep. Rate 250, 125, 50 kHz: user operation 1, 2, 5 kHz: diagnostic

18. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE BEAM PARAMETER MEASUREMENT Schottky scan – energy & energy spread screen DV04 (YAG) 4.4 m from cathode screen DV05 same optical path as DV04 -160°, σ x = 600 µm energy energy spread 15 pC

19. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE BEAM PARAMETER MEASUREMENT Transverse Emittance – Solenoid scan screen DV02screen DV01 solenoid for emittance compensation, field precisely measured not suitable for space-charge dominated beams, preliminary method as long as the analysis tools for the installed slit mask method are under development Measurement: 5 MV/m gradient 2 MeV energy laser: temporal:15 ps FWHM Gaussian lateral: 2.7 mm diam. sharp edges launch phase & pulse energy variation -160° 20 pC σ x = 320 µm

20. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE BEAM PARAMETER MEASUREMENT Transverse Emittance – Solenoid scan launch phase scan – search for optimum - 160° Φ laser = 20° bunch charge dependence

21. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE SUMMARY First Run of SRF Gun operation: about 100 h with Cu cathode, 400 h with Cs 2 Te I av = 1 µA, total 15 C (diagnostic mode & radiation safety permission) Problems during commissioning: Cavity cleaning and low gradient wrong cavity π-mode frequency at 2 K (will be corrected in shut-down) high level of microphonics due to membrane pumps (solved) tuners have hysteresis (will be repaired in shut-down) insufficient vacuum in cathode transfer system (improved in shut-down) Answers to the „big“ questions: basic principle (NC photo cathode) works well no limits found, results agree with predictions high current operation: answer will be given in the first run in 2009 high gradient and brightness: needs an improved cavity Future: Oct.- Jan. 09: correction of π-mode frequency 2009: connection to ELBE, run with high current fabrication of two improved cavities, funded by BMBF, replacement in 2010

22. Institute of Radiation Physics Jochen Teichert www.fzd.de Forschungszentrum Dresden-Rossendorf Radiation Source ELBE Acknowledgements We acknowledge the support of the European Community-Research Infrastructure Activity under the FP6 “Structuring the European Research Area” programme (CARE, contract number RII3-CT-2003-506395) and the support of the German Federal Ministry of Education and Research grant 05 ES4BR1/8. THANK YOU FOR YOUR ATTENTION Thanks to the ELBE crew, the technical staff of BESSY, DESY and MBI, to ACCEL and all the others supported and encouraged this project