Free Electron Laser Commissioning Meeting

Friday, 10 Apr 98
Recorder: C. Bohn

Next Meeting


Date: 17 Apr 98
Time: "0845"-0945
Place: FEL Facility Break Room

Agenda for Next Meeting


Item Person Responsible Time ---- ------------------ -------- Status of Open Action Items All 5 min Scheduling and Commissioning Program Bohn/All 50 min New Issues All 5 min

This Week's Attendees


J. Bennett, S. Benson, J. Bisognano, C. Bohn, J. Boyce, D. Douglas, M. Drury, F. Dylla, J. Fugitt, A. Grippo, L. Harwood, R. Lauze, R. Li, L. Merminga, G. Neil, D. Oepts, M. Shinn, R. Walker

Closed Action Items


Items of Discussion


This week's activities involved running high-average-current beam to the straight-ahead dump and doing parametric studies of the transverse emittance at the exit of the cryounit using one of the multislit diagnostics. As of this writing (1150, 10 April 1998), we are running 38 MeV beam at about 1 mA stably. With 60 pC bunch charge, the nominal normalized transverse emittance at the exit of the cryounit was measured to be about 6 mm-mrad in both the horizontal and vertical directions. By comparison, PARMELA simulations predict 3.5 mm-mrad. Basically we are off to a good start, but as noted below, we still need to decide how to optimize the injector setup and what constitutes an adequate setup. The answer lies ultimately in the beam quality at the entrance to the cryomodule, and it awaits availability of both the multislit diagnostic and bunch-length monitor at that point. The week's activities also permitted us to verify operability of all of the beam position monitors and the current-monitor cavity on the straight-ahead machine.

There is concern about alignment of injector components. This week we moved the second solenoid down about 0.5 cm which enabled us to center beam through the buncher cavity, both solenoids, and the cryounit. Before moving the solenoid, we could not center through it but could center through the other components (or so it appeared). C. Bohn will set up an off-line meeting to identify key measurements that will lead to resolution. All agreed that we need to harden the injector setup and then "not touch it".

There was some discussion about next week's shift plans. As it stands now, we will run sustained high cw current (hopefully 1.1 mA) to the straight-ahead dump for three reasons: to monitor cathode lifetime systematically, to watch for infant mortality, and to ensure our high-power rf systems stay stable, especially the "8 kW" cryomodule klystrons. We also have extensive time dedicated to diagnostics checkout next week.

Regarding staffing for shifts, we will have two FEL'ers and one CEBAF operator on every shift next week (from 0800 Monday through 2400 Friday, with Thursday day shift allocated to installation). Beginning the following week, on 20 April, we will have only one FEL'er (with another FEL'er on standby in case of emergency) and one CEBAF operator assigned to each shift. Assignments for the next two weeks are:

13-17 April 1998:
Owl -- Bohn, Hill, CEBAF operator
Day -- Siggins, Merminga, CEBAF operator
Swing -- Krafft, Shinn, CEBAF operator
20-24 April 1998:
Owl -- Jordan, CEBAF operator, Piot on standby
Day -- Yunn, CEBAF operator, Li on standby
Swing -- Neil, CEBAF operator, Oepts on standby

C. Bohn led a discussion to delineate prerequisites to inserting the wiggler and trying to get first light. Their "due date" is 1 May 98, which is the day the wiggler will be installed per the present schedule. Prospects are reasonably good that we will be able to meet that schedule! The prerequisites are as follows (they all have the same priority!):

1. Support of CEBAF operators. Start using them NOW!
2. Stable 1.1 mA, 38 MeV beam.
3. Good (>10 hr) cathode lifetime.
4. Working diagnostics.

5. Adequate injector setup.
6. Working Analog Monitoring System.
7. Detailed procedures and test plans well communicated to MCC staff (of which we have a good start courtesy of S. Benson).
8. Working optical transport, including Laser Safety System for the Optical Control Room.
9. Great teamwork with some individual sacrifice ("individual" was not named at this meeting).

R. Lauze and J. Fugitt highlighted some needs that have arisen as a consequence of commissioning from the MCC (which started 6 April as planned!). A list follows:

Other needs discussed off-line include an FEL Bugger Log that will be kept in the MCC Control Room, which Bohn has already placed there, and an FEL Operator Limits Log. Bohn envisions devising the latter once we have a solution for 1.1 mA cw, 38 MeV beam into the straight-ahead dump. His thinking is to use that setup as a starting point for configuration control following discussions of the matter at previous FEL Commissioning Meetings.

New Issues


L. Merminga raised the question whether the procedure for ramping up the current needs revision. Based on how the tuners work, she is leaning toward first setting the cryomodule cavities on crest, then ramping the current, then taking the cavities off crest per Yunn's PARMELA parameters. Eventually the magnetostrictive tuners will be working well enough to make this a moot issue, but for now it is relevant. She will work to answer this question early next week.

New Action Items


Old Action Items


Procedures in Work


Emittance Growth from CSR

Thread Beam around Machine, Top-Level           Douglas, finalize 6 Mar 98
RF Stability during Energy Recovery             Merminga, 6 Mar 98
MPS/BLM Checkout for First Light                Mahoney, 8 Apr 98