Free Electron Laser Commissioning Meeting

Friday, 21 Nov 97
Recorder: C. Bohn

Next Meeting


Date: 5 Dec 97
Time: 0830-0930
Place: FEL Facility Break Room

Agenda for Next Meeting


Item Person Responsible Time ---- ------------------ -------- Status of Action Items All 5 min Progress Report on Commissioning Legg/Bohn 15 min Scheduling Update Bohn 15 min CW Setup Legg 15 min New Issues All 5 min Agenda for next week All 5 min

This Week's Attendees


J. Bennett, G. Biallas, C. Bohn, D. Douglas, D. Engwall, J. Fugitt, K. Jordan, G. Krafft, R. Legg, L. Merminga, G. Neil, P. Piot, J. Preble, Q.-S. Shu, B. Yunn

Closed Action Items


The following actions from last week's report were closed out:

Items of Discussion


As mentioned last week, commissioning over Thanksgiving break and weekend will be on a voluntary basis, with no formally established shift assignments. Work on Thanksgiving Day remains verboten! Plans for this weekend call for diagnostics checkout, and if all requisite installation is completed, we plan to run beam through the cryomodule into the energy-recovery dump next week. If not, we will do more injector commissioning. As is oft repeated, we must run tune-up beam to the first-light dump before Christmas in preparation for timely GEN target production.

R. Legg and J. Preble presented this week's commissioning highlights:

L. Merminga presented data on rf phase and amplitude noise in both the cryounit and the cryomodule. The unregulated phase noise (microphonics) is dominated by 60 Hz. The open-loop (unregulated) phase noise is about 1.5 degrees rms in a typical cavity. This is about three times larger than in CEBAF, but it is almost entirely compensated by lower external Q and is accordingly not a problem. Presumably the source of the 60 Hz is a multiplicity of pumps. Regulated phase noise is about 0.004 degrees rms in a typical cavity. Unregulated amplitude noise (dV/V) is typically about 1%, but regulation reduces it typically below 0.01%, i.e., below 10^-4. However, there are strong peaks in the regulated amplitude noise at 60 Hz, so noise correlation could conceivably occur. If desired in the future, we can probably reduce the noise by adjusting the pumps. The Lorentz coefficient (ponderomotive force) in the cryomodule cavities was also measured and found acceptable.

G. Neil followed with a presentation of a draft plan to investigate the sensitivity of the FEL to off-normal machine settings, a post-lasing activity. The basic idea is to identify the most important parameters to monitor and adjust during user experiments with the laser. Neil proposed investigating lasing sensitivity with respect to a number of parameters, including: bunch charge (which will surely drop as cathode quantum efficiency drops), solenoid focusing in the gun (which Yunn has already identified as sensitively driving beam properties at the wiggler), buncher cavity settings, cryounit cavity settings, cryomodule cavity settings, mismatch of electron beam to wiggler, missteering of electron beam through wiggler, missteering of optical-cavity mode, detuning of optical cavity, and variations in electron-beam energy. He anticipates the totality of the study will require about four months. Of course, we will learn much during prelasing commissioning about the sensitivity of electron-beam properties at the wiggler location vs. machine settings. Neil is going to provide D. Oepts of FOM, Netherlands, a copy of the draft plan to solicit his input. Oepts already has a copy of the existing lasing procedures. (Note: Oepts, a seasoned FEL expert, is scheduled to arrive in mid-January 1998 for a one-year sabbatical.)

New Issues


As mentioned above, measured electron-beam momentum out of the injector is lower than was anticipated based on srf-measured cavity gradients. We need to understand why. Is it due to, e.g., miscalibration of the cavities and/or the field map of the (first) DU magnet that was used to make the measurement?

New Action Items


Old Action Items


None.

Procedures in Work


First Light Setup

Emittance Growth from CSR

Thread Beam around Machine, Top-Level           Douglas, 1 Dec 97