Free Electron Laser Commissioning Meeting

Friday, 16 Jan 98
Recorder: C. Bohn

Next Meeting


Date: 23 Jan 98
Time: 0830-0930
Place: FEL Facility Break Room

Agenda for Next Meeting


Item Person Responsible Time ---- ------------------ -------- Status of Open Action Items All 10 min Progress Report on Commissioning Preparations Bohn/All 40 min New Issues All 5 min Agenda for next week All 5 min

This Week's Attendees


J. Bennett, S. Benson, G. Biallas, J. Bisognano, C. Bohn, D. Douglas, D. Engwall, A. Hofler, K. Jordan, G. Krafft, R. Legg, R. Li, L. Merminga, G. Neil, P. Piot, J. Preble, Q.-S. Shu, R. Walker

Closed Action Items


  • Bohn: Meet with R. Lauze to begin planning for operator support. Status: Done -- See Items of Discussion below.

    Items of Discussion


    We reviewed progress on the key tasks that need to be accomplished prior to resuming commissioning (installation activities, listed in last week's minutes, are being tracked via other venues):

  • Task: Prepare for Commissioning from MCC (Bohn)
    Status: Bohn met with R. Lauze on 13 Jan 98. MCC operators are projected to turn on CEBAF starting 5 Feb 98. It is unlikely that we could use an operator prior to mid-February, but this conclusion is pending success with the turn-on. Hardware for the MCC (two workstations and a video system) is still projected to be installed prior to 26 Jan 98. R. Legg is conducting a tour and tutorial of the FEL machine for CEBAF operators in the next week that will be filmed.
  • Task: Align Injector Components (Legg)
    Status: The cryounit alignment has been verified to be good to within 1 mm, both with respect to the cryostat itself, and with respect to the alignment of the cavities, including tilt, inside the cryostat. However, an internal valve was not completely closed, subtending into the beam aperture a distance somewhere between 0.95 cm and 1.1 cm. During the December runs this necessitated steering around the blockage, and presently it is thought that the concomitant beam "misalignment" was responsible for the observed distortion of the beam's transverse phase space.
  • Task: Complete MPS for First Light (Jordan)
    Status: Remaining is the need to interface the defocusing quads and raster magnets and finish instrumenting the dumps. Jordan estimates that the MPS necessary to run 1.1 mA cw in the injection line to the 0G dump will be in place by month's end, and that needed to run 1.1 mA cw to the straight-ahead (2G) dump will be in place by mid-February, both commensurate with the commissioning schedule.
  • Task: Complete First-Light Magnet Field Maps (Douglas)
    Status: The field maps in question pertain to the QB and QG quadrupoles. Generic field maps for both are in hand but need to be installed. G. Biallas, as system owner, will take care of this.
  • Task: Complete First-Light BPM Preparations (Krafft)
    Status: The 4-channel BPMs are certified to be accurate at the 0.1-mm level with 60 pC bunches. They will not be as accurate with 1 pC bunches, for which they can be used as peg points with 0.5-mm-level accuracy. A software rewrite has been done respective to the SEE BPMs (on schedule) that will enable inputting their correct calibration curves.
  • Task: Finish and Install Bunch-Length Monitors (Jordan)
    Status: Uwe Happek's student, Mr. James, will be here in early February to do checkout. James wrote the software for the bunch-length monitors. Their stands are installed, and their boxes are ready, but we don't yet have confirmation from Happek himself that the interferometers will be here soon. G. Krafft is trying to close this loop.

    G. Neil advised that the optical cavity might not be completed by the end of the month. The alignment pellicles will need to be redesigned and reinstalled, an activity that, if not completed before commissioning begins anew, could take place in mid-February when the GEN target chamber is installed.

    J. Preble indicated that, with the installation of new warm windows on the injector cryounit, he suspected we will be able to run with the "old" nominal cavity gradients of 9 MV/m in the first cavity and 11 MV/m in the second. He advised that we can assume these gradients in developing injector-related procedures.

    R. Legg convened a meeting on 12 Jan 98 to discuss strategies for optimizing injector beam quality. The motivation was the high transverse emittance, exceeding 20 mm-mrad, measured on the last shift prior to December shutdown. As noted above, the cause of the bad emittance might have been the valve internal to the cryounit, but the need for an optimization procedure exists nonetheless. The basic plan is 3-fold:

    1. Finish alignment checkout (results of which are discussed above),
    2. Codify the existing collection of 3D PARMELA runs, of which there is an extensive set of "9,11 MV/m" runs,
    3. Set up the injector using the procedures already written, but incorporate adjustments as necessary based on inferences from 1 and 2 above. Sensitive "knobs" available for 3 above include the solenoids at the gun (especially the first one), the buncher phase (combined with the cryounit cavity phases), the beam spot size, and the cavity gradients. It could conceivably be useful, as a troubleshooting guide, to turn off cavity 1 or 2, successively, and measure the transverse emittance with the multislit diagnostic. Perhaps this would identify the source of emittance growth as one of the cavities. We also could try a solenoid scan in front of the cryounit to check beam quality there, but this technique is probably good only for "zero" bunch charge.
    A discussion of FEL inputs to the SWIS followed. Recommendations are that during commissioning the SWIS indicates verbal indication of the status of the FEL vault and general commissioning activity/goal, and after we start delivering laser beam to users, it indicates laser power and which of the user labs is receiving light. These recommendations seem to satisfy the main purpose of the SWIS, namely, to provide a service to our users. Bohn will feed these suggestions back to D. Windmueller.

    New Issues


    New Action Items


    Old Action Items


    Procedures in Work


    First Light Setup
    
    Emittance Growth from CSR
    
    Thread Beam around Machine, Top-Level           Douglas, finalize 31 Jan 98
    RF Stability during Energy Recovery             Merminga, 23 Jan 98
    MPS/BLM Checkout for First Light                Jordan, 23 Jan 98