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LCLS

Experience with the LCLS RF Guns D. H. Dowell et al. DOE Status Meeting for the LCLS May 13, 2008. LCLS. Talk Outline. General Description of the LCLS Gun Operational Experience with Gun1 RF Processing of Gun2 Gun1 RF Probe Upgrade and Beamline Component Repairs & Alignment Summary.

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LCLS

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  1. Experience with the LCLS RF GunsD. H. Dowell et al.DOE Status Meeting for the LCLSMay 13, 2008 LCLS

  2. Talk Outline • General Description of the LCLS Gun • Operational Experience with Gun1 • RF Processing of Gun2 • Gun1 RF Probe Upgrade and Beamline Component Repairs & Alignment • Summary

  3. 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 racetrack design ANSIS model of thermal profile D. Dowell V. Dolgashev E. Jongewaard B. Kirby J. Lewandowsky R.F. Boyce C. Limborg Z. Li A. Vlieks J. Schmerge J. Wang L. Xiao no quad. fields

  4. RF Gun1 Installed in March 2007 dual feed

  5. 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 2mm • The real emission is very non-uniform • Electron emission image resolves details as small as ~10 microns Slide compliments of C. Limborg

  6. Scan of Emittance at 1 nC vs. Gun Solenoid Gun Emittance Optimization:Established Tune-up Procedure for Gun & Injector Correlation Plot GUI compliments of H, Loos, SLAC

  7. Bunch Length Depends upon Laser Size Measurements performed at 250 pC using TCAV0 & OTR2 (135 MeV) Used to determine operating point for BC1 compression

  8. 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 Gun2 RF high-power test • Replace Gun1 probes with new probes • Repair, align & replace other beamline components during a 2-week April down

  9. Gun2 RF Processing • Goal to process Gun2 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 Gun2 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

  10. ~600 watts, ave Comparison of Old and New Probes Current Gun1 Probe New Probe in Gun2 New probes have 76.6-80.7 dB coupling in Gun2 Old probes have 55-60 dB coupling

  11. Comparison of the New Probes During RF Processing of Gun2

  12. Comparison of the Cathode Field Based on Dissipated Power and Gun FWD Power

  13. Just Completed Shutdown (April 10-27) to Upgrade Gun and Repair Beamline Components • Goals of April Downtime • Replace gun probes • Repair & Realign GTL diagnostics • IM01 toroid • FC01 faraday cup • Replace in-vacuum laser mirrors & window • Re-install laser alignment mirror • Correct rotation of TCAV • Replace VV03

  14. Replacement of Gun Probes for 120 Hz Operation Old Probes New Probes

  15. Repair/Replacement of Gun-to-Linac Components The GTL In-vacuum Laser Mirrors YAG01/FC01 IM01 Toroid

  16. Recovery of Injector Vacuum After Venting GTL-Vacuum Both Pumps on Same Supply Initial Pumpdown Gun RF Processing Gun Vacuum Repaired Ion Pump Cable

  17. Good Signals from New Probes

  18. QE Initially 3 to 4 Times Lower than Before the Vent Before After

  19. 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

  20. Electron emission and white light images show minor changes to cathode surface After Venting Gun Before Venting Gun Electron Emssion Images White Light Images

  21. OTR2 Image & Slice Emittance Measurement Show the TCAV is Now Aligned

  22. Summary • Gun1 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) • Gun1 operation limited to 30 Hz due to probe heating (fixed with probe change) • New probe design validated in Gun2 high-power processing in Klystron Lab • Gun2 & solenoid RF-processed to 125MV/m, 120Hz, 2 microseconds • Aligned and ready as a spare gun-assembly. • Gun1 probes replaced and beamline components repaired during April 10-27 scheduled downtime • Gun1 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: OTR2 emittance < 1.2 microns on first measurement! • High energy beam, 13.6 GeV, established within 6 hours of turn-on • Excellent beam operation since re-start, especially during first weekend

  23. 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

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