Free Electron Laser Commissioning Meeting

Friday, 13 Feb 98
Recorder: C. Bohn

Next Meeting


Date: 20 Feb 98
Time: 0830-0930
Place: FEL Facility Break Room

Agenda for Next Meeting


Item Person Responsible Time ---- ------------------ -------- Status of Open Action Items All 5 min Status of Gun Legg 10 min Optimal 60 pC Setup Yunn 20 min Configuration Control Bohn 10 min Procedures in Work All 5 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, F. Dylla, J. Fugitt, A. Hofler, K. Jordan, G. Krafft, R. Legg, R. Li, L. Merminga, P. Piot, J. Preble, M. Shinn, Q.-S. Shu, T. Siggins, R. Walker, B. Yunn

Closed Action Items


Items of Discussion


R. Legg summarized what is known from the gun's autopsy to date. The cathode has global particulates and a few localized splotches. Spectroscopy results obtained by Legg and L. Doolittle in the Test Lab indicate the presence of Cu and Fe, as well as several other elements. There is no evidence of pitting; the observations suggest arcing and/or sputtering occurred. The cathode will now be sent to William and Mary for auger analysis. We will open the gun and examine the ball, tube, and anode plate to acquire information for diagnosing the cause of the problem. In parallel, we will measure tolerances to check for any drooping of the structures that might have occurred.

The present estimate is that we will resume commissioning with beam on 2 Mar 98. Bohn plans to staff shifts in the same way as had been planned for the 5 Feb 98 startup, with the exception that the "3-shift" mode will be in effect for everyone from the beginning. R. Walker will prepare the revised shift plan and distribute it probably late next week, by which time we should be more confident of the actual start date. Latest word from J. Boyce is that, as long as we irradiate the GEN targets sometime in March, Physics Division is content.

C. Bohn presented plans for training people on the FEL control system. He is trying to arrange for not only the "FEL commissioning team" to attend, but also as many CEBAF operators as possible. Thus, the dates of the classes are not yet firm, other than that they will occur before we begin to run beam. Bohn will publish an agenda early next week.

New Issues


B. Yunn has developed optimized machine settings for both 60 pC and 135 pC bunches. During the week, and at this meeting, the question arose concerning which one to use. The 135 pC settings will "work" at 60 pC, and were they to be used, that would eventually save time by circumventing the need to commission "twice", once for each bunch charge. Consequently, Bohn had been disposed toward using the 135 pC settings. However, Yunn mentioned this morning that the peak current for first light would be about twice as high if the optimal 60 pC settings were used. Correspondingly, the FEL gain would be about twice as high, lending much more confidence in successful lasing. On the other hand, there would not be as much flexibility a priori for CSR experiments were the settings "limited" to 60 pC. The upshot of the discussion is that we are building a laser, and we need to do everything within reason to assure success in lasing. So, we should plan to use the 60 pC optimal settings, and R. Li and D. Douglas should look at implications for CSR experiments by continuing their modeling. (Note -- a very tentative statement -- It might conceivably be possible to do a "quick" setup at 135 pC when we want to do CSR experiments since we would not need to optimize beam brightness at the wiggler location for that purpose. We will learn more as we turn on the machine.) Plans for next week's meeting (as implied in the agenda) are to adopt baseline settings and freeze them so everyone can be aligned on the precise program for near-term commissioning.

New Action Items


Old Action Items


Procedures in Work (will update status at next meeting)


Emittance Growth from CSR

Thread Beam around Machine, Top-Level           Douglas, finalize 27 Feb 98
RF Stability during Energy Recovery             Merminga, 6 Feb 98
MPS/BLM Checkout for First Light                Jordan, 6 Feb 98