Experience with the LCLS RF Guns D H

Experience with the LCLS RF Guns D. H. Dowell et al. DOE Status Meeting for the LCLS May 13, 2008 LCLS May 14, 2008 Experience with RF Guns 1 David Dowell dowell@slac. stanford. edu

Talk Outline General Description of the LCLS Gun Operational Experience with Gun 1 RF Processing of Gun 2 Gun 1 RF Probe Upgrade and Beamline Component Repairs & Alignment Summary May 14, 2008 Experience with RF Guns 2 David Dowell dowell@slac. stanford. edu

LCLS RF Photo-Cathode Gun 1. 6 -cell S-band (2856 MHz - BNL/SLAC/UCLA) Copper cathode 120 -Hz repetition rate 140 -MV/m cathode field (max) Axially symmetric RF fields 15 MHz 0 -p mode separation Dual RF-feed Built at SLAC dual feed May 14, 2008 Experience with RF Guns racetrack design no quad. fields ANSIS model of thermal profile D. Dowell V. Dolgashev E. Jongewaard B. Kirby J. Lewandowsky R. F. Boyce 3 C. Limborg Z. Li A. Vlieks J. Schmerge J. Wang L. Xiao David Dowell dowell@slac. stanford. edu

RF Gun 1 Installed in March 2007 dual feed May 14, 2008 Experience with RF Guns 4 David Dowell dowell@slac. stanford. edu

White Light (left) and Electron Emission (right) Images of the LCLS Gun Cathode Established procedure for documenting cathode uniformity, Part of the daily laser checkout 2 mm • The real emission is very non-uniform • Electron emission image resolves details as small as ~10 microns May 14, 2008 Slide compliments of C. 5 Limborg Experience with RF Guns David Dowell dowell@slac. stanford. edu

Gun Emittance Optimization: Established Tune-up Procedure for Gun & Injector Scan of Emittance at 1 n. C vs. Gun Solenoid May 14, 2008 Correlation Plot GUI compliments of H, Loos, SLAC Experience with RF Guns 6 David Dowell dowell@slac. stanford. edu

Bunch Length Depends upon Laser Size Measurements performed at 250 p. C using TCAV 0 & OTR 2 (135 Me. V) Used to determine operating point for BC 1 compression May 14, 2008 Experience with RF Guns 7 David Dowell dowell@slac. stanford. edu

LCLS Gun Summary and Upgrade Plan Gun has operated reliably for the past year Beam parameters meet the LCLS specifications Initial problem of low QE resolved with “active” and “passive” laser cleaning. Produced non-uniform emission…acceptable for now Gun operation limited to 30 Hz due to overheating RF probes Gun Probe Upgrade Plan: Test new probes during Gun 2 RF high-power test Replace Gun 1 probes with new probes Repair, align & replace other beamline components during a 2 week April down May 14, 2008 Experience with RF Guns 8 David Dowell dowell@slac. stanford. edu

Gun 2 RF Processing Goal to process Gun 2 to 120 MV/m, 120 Hz Test of the new RF probe design Tests were performed in the Klystron Asta bunker using RF from Test Stand 1 Summary of Gun 2 RF Processing Initial trouble with the dual window assembly Removed, inspected & tested windows. Found no problem with windows Installed new windows in assembly and resumed conditioning Observed same problem, conditioned through it Achieved full gradient, 120 Hz, validated new probe design May 14, 2008 Experience with RF Guns 9 David Dowell dowell@slac. stanford. edu

Comparison of Old and New Probes Current Gun 1 Probe New Probe in Gun 2 ~600 watts, ave New probes have 76. 6 -80. 7 d. B coupling in Gun 2 Old probes have 55 -60 d. B coupling May 14, 2008 Experience with RF Guns 10 David Dowell dowell@slac. stanford. edu

Comparison of the New Probes During RF Processing of Gun 2 May 14, 2008 Experience with RF Guns 11 David Dowell dowell@slac. stanford. edu

Comparison of the Cathode Field Based on Dissipated Power and Gun FWD Power May 14, 2008 Experience with RF Guns 12 David Dowell dowell@slac. stanford. edu

Just Completed Shutdown (April 10 -27) to Upgrade Gun and Repair Beamline Components • Goals of April Downtime – Replace gun probes – Repair & Realign GTL diagnostics • • IM 01 toroid FC 01 faraday cup Replace in-vacuum laser mirrors & window Re-install laser alignment mirror – Correct rotation of TCAV – Replace VV 03 May 14, 2008 Experience with RF Guns 13 David Dowell dowell@slac. stanford. edu

Replacement of Gun Probes for 120 Hz Operation Old Probes New Probes May 14, 2008 Experience with RF Guns 14 David Dowell dowell@slac. stanford. edu

Repair/Replacement of Gun-to-Linac Components The GTL In-vacuum Laser Mirrors YAG 01/FC 01 IM 01 Toroid May 14, 2008 Experience with RF Guns 15 David Dowell dowell@slac. stanford. edu

Recovery of Injector Vacuum After Venting GTL-Vacuum Both Pumps on Same Supply Initial Pumpdown Gun RF Processing Gun Vacuum Repaired Ion Pump Cable May 14, 2008 Experience with RF Guns 16 David Dowell dowell@slac. stanford. edu

Good Signals from New Probes May 14, 2008 Experience with RF Guns 17 David Dowell dowell@slac. stanford. edu

QE Initially 3 to 4 Times Lower than Before the Vent Before May 14, 2008 Experience with RF Guns After 18 David Dowell dowell@slac. stanford. edu

QE is Slowly Increasing -Low Level Laser Cleaning. Gun-Vacuum QE QE has risen a factor of ~1. 8 since re-starting operations on April 28 The plotted QE is determined at the peak of the Schottky scan May 14, 2008 Experience with RF Guns 19 David Dowell dowell@slac. stanford. edu

Electron emission and white light images show minor changes to cathode surface Electron Emssion Images After Venting Gun Before Venting Gun White Light Images May 14, 2008 Experience with RF Guns 20 David Dowell dowell@slac. stanford. edu

OTR 2 Image & Slice Emittance Measurement Show the TCAV is Now Aligned May 14, 2008 Experience with RF Guns 21 David Dowell dowell@slac. stanford. edu

Summary Gun 1 has operated reliably at 30 Hz for the past year. Beam quality meets LCLS requirements. Initial low QE increased due to laser cleaning. Laser cleaning resulted in non-uniform emission Investigating less aggressive cleaning process (Axel Brachmann) Gun 1 operation limited to 30 Hz due to probe heating (fixed with probe change) New probe design validated in Gun 2 high-power processing in Klystron Lab Gun 2 & solenoid RF-processed to 125 MV/m, 120 Hz, 2 microseconds Aligned and ready as a spare gun-assembly. Gun 1 probes replaced and beamline components repaired during April 10 -27 scheduled downtime Gun 1 and other RF re-processed in two-days! Beam operations re-established within 6 -hours! QE ok and slowly rising GTL vacuum still ~2 -times pre-work value, but coming down. New probes are being used to regulate gun RF Beam quality same as before venting: OTR 2 emittance < 1. 2 microns on first measurement! High energy beam, 13. 6 Ge. V, established within 6 hours of turn-on Excellent beam operation since re-start, especially during first weekend May 14, 2008 Experience with RF Guns 22 David Dowell dowell@slac. stanford. edu

And Thanks to Everyone for making the April Down a Success! Klystron Department: Erik Jongewaard, John Eichner, Arnold Vielks The SLAC Vacuum Group: Mike Robertson, Ted Martinez, Mike Thomas, Mark Bostic, Tito Torres, Oscar Guerra, Daniel Peterswright, Jeff Robert, John O’Neal Precision Alignment: Mike Gaydosh, Francis Gaudreault, Hans Imfeld, Mike Rodgers and Bryan Rutledge Controls: Kristi Luchini, Ken Brobeck, Terri Lahey Laser: Greg Hays, Sasha Gilevich, Philippe Hering, Alan Miahnahri And Especially: Phil Cutino who planned and orchestrated the downtime work May 14, 2008 Experience with RF Guns 23 David Dowell dowell@slac. stanford. edu