1. David H. Dowell dowell@slac.stanford.edu RF Gun Commissioning LCLS FAC April 16, 2007 1 RF Gun Commissioning Experience David H. Dowell for the LCLS Injector Team Facility Advisory Committee Meeting April 16, 2007 Description of Gun Design & Parameters Results of Gun High-Power Tests in Klystron Lab Installation at S20 and Pre-Beam Testing First Photo-Beam! Results & Observations of Initial Gun Commissioning Summary

2. David H. Dowell dowell@slac.stanford.edu RF Gun Commissioning LCLS FAC April 16, 2007 2 Z-coupling: reduces pulsed heating increases vacuum pumping Racetrack to minimize quadrupole fields Deformation tuning to eliminate field emission from tuners Iris reshaped reducing field 10% below cathode Increase 0-pi mode separation to 15MHz All 3D features included in modeling: laser port and pickup probes 3D fields used in Parmela simulation 3D RF Design of Gun RF Parameters f0 (GHz)2.855987 Q013960 β2.1 Mode Sep.  f (MHz) 15 E0:E10.999:1 Slide Compliments of Z. Li & L. Xiao C. Limborg et al., “RF Design of the LCLS Gun”, LCLS-TN-05-3 L. Xiao et al., “Dual feed rf gun design for the LCLS,” Proc. 2005 Particle Acc. Conf.

3. David H. Dowell dowell@slac.stanford.edu RF Gun Commissioning LCLS FAC April 16, 2007 3 Gun-Solenoid Assembly Cut-away view of LCLS Gun Cathode weld assembly August 2005 LCLS RF Gun Mechanical Design Review Compliments E. Jongewaard

4. David H. Dowell dowell@slac.stanford.edu RF Gun Commissioning LCLS FAC April 16, 2007 4 Gun Design and Measured Specifications RF ParametersDesignMeasured f  (GHz) 2.8559872.855999 Q01396013900 β2.12.03 Mode Sep.  f (MHz) 1515.17 Field Balance11 Measurements compliments of J. Wang and J. Lewandowski

5. David H. Dowell dowell@slac.stanford.edu RF Gun Commissioning LCLS FAC April 16, 2007 5 Conditioning Time to 120 MV/m & Dark Charge per RF Pulse High-Power Gun1 Test in Klystron Lab

6. David H. Dowell dowell@slac.stanford.edu RF Gun Commissioning LCLS FAC April 16, 2007 6 Results of Gun High-Power Tests in Klystron Lab: Only concern is the heating of the RF probes Probe external temperatures during Nov 9 conditioning to 120MV/m Upper probe temperature and calibration vs. RF power Therefore, the gun rate will be limited to 30 Hz during 2007 Commissioning. New probes for Gun 2 will have -75dB coupling and be copper plated.

7. David H. Dowell dowell@slac.stanford.edu RF Gun Commissioning LCLS FAC April 16, 2007 7 Lowering the Gun-Solenoid Assembly into the Sector 20 Injector Vault

8. David H. Dowell dowell@slac.stanford.edu RF Gun Commissioning LCLS FAC April 16, 2007 8 Gun-Solenoid Assembly is Home!

9. David H. Dowell dowell@slac.stanford.edu RF Gun Commissioning LCLS FAC April 16, 2007 9 Measurements: J. VanPelt, A. Vlieks, J. Wang, C. Rivetta Pre-Beam RF Measurements and Water System Test

10. David H. Dowell dowell@slac.stanford.edu RF Gun Commissioning LCLS FAC April 16, 2007 10 Gun Processed at Sector 20 to Nominal RF Power Thanks to R. Akre, B. Hong

11. David H. Dowell dowell@slac.stanford.edu RF Gun Commissioning LCLS FAC April 16, 2007 11 First Photo-Electrons!!! It Works!!! Dark Charge Images of First Photo-Electrons April 5, 2007 Photo-Electrons: After adjusting laser-gun phase

12. David H. Dowell dowell@slac.stanford.edu RF Gun Commissioning LCLS FAC April 16, 2007 12 Early Images of Beam on Yag01 (Gun Exit) and Yag02 (Entrance to L0a) YAG01 YAG02

13. David H. Dowell dowell@slac.stanford.edu RF Gun Commissioning LCLS FAC April 16, 2007 13 Optimized Macropulse Timing in RF Waveform by Measuring Beam Energy vs. Gun Delay RF Delay (ns) Beam Momentum (GeV/c) Set Timing Here for Max Energy Used measurement to calibrate RF system (Gun RF probes)

14. David H. Dowell dowell@slac.stanford.edu RF Gun Commissioning LCLS FAC April 16, 2007 14 Schottky Scan of Gun Phase Relative to Laser Zero Crossing of RF Field Optimum Launch Phase 30deg Measurement: H. Loos, April 13, LCLS e-log

15. David H. Dowell dowell@slac.stanford.edu RF Gun Commissioning LCLS FAC April 16, 2007 15 Beam Charge vs. Drive Laser Energy & Launch Phase: Schottky Enhancement of QE Launch Phase at 30 degrees Launch Phase at 85 degrees from zero crossing

16. David H. Dowell dowell@slac.stanford.edu RF Gun Commissioning LCLS FAC April 16, 2007 16 Regen pockel cell delay = 300.0680 microSec Regen pockel cell delay = 300.0650 microSec Precise Adjustment of Regenerative Amplifier Pockel Cell Timing is Crucial measurements: B. White et al., LCLS e-log, April 11, 2007

17. David H. Dowell dowell@slac.stanford.edu RF Gun Commissioning LCLS FAC April 16, 2007 17 YAGG1, Gun Spectrometer ~100keV YAG01, ~50cm from cathode YAG02, ~80cm from cathode Beam Momentum = 4.3 MeV/c measurements: H. Loos & J. Welch, LCLS e-log, April 13, 2007

18. David H. Dowell dowell@slac.stanford.edu RF Gun Commissioning LCLS FAC April 16, 2007 18 Virtual Cathode Camera YAG01 E-Beam Appears to Preserve the Laser’s Spatial Fluctuations Laser Image: S. Gilevich et al., LCLS e-log, April 2007

19. David H. Dowell dowell@slac.stanford.edu RF Gun Commissioning LCLS FAC April 16, 2007 19 YAG01 YAG02 Images compliments of P. Emma & R. Iverson, LCLS e-log, April 13, 2007 YAG03 L0a Gun & Solenoid Evolution of Beam Along Injector

20. David H. Dowell dowell@slac.stanford.edu RF Gun Commissioning LCLS FAC April 16, 2007 20 Summary Gun is operational at Sector 20: RF conditioning complete Water temp and LLRF control loops operating Providing beam for injector commissioning High level S/W applications being implemented Technical Issues: Gun RF probe heating limits gun operation to 115MV/m and 30 Hz. This is fixed on Gun2. Progress hindered by non-functioning, critical diagnostics!! QE is 2 to 4 times lower than expected Plan for cathode cleaning Gun-Solenoid assembly appears to be pointing down and to right