Free Electron Laser Commissioning Meeting
Friday, 31 Oct 97
Recorder: C. Bohn
Next Meeting
- Date: 7 Nov 97
- Time: 0830-0930
- Place: FEL Facility Break Room
Agenda for Next Meeting
Item Person Responsible Time
---- ------------------ --------
Review of Minutes/Errata All 5 min
Scheduling Update Bohn 15 min
Progress Report on Injector Commissioning Legg 5 min
Schedule/Requirements for GEN Target Prep Boyce 10 min
Procedure for Threading to First-Light Dump Douglas 15 min
New Issues All 5 min
Agenda for next week All 5 min
This Week's Attendees
S. Benson, G. Biallas, J. Bisognano, C. Bohn, J. Boyce, D. Engwall, G.
Krafft, A. Grippo, R. Legg, R. Li, L. Merminga, P. Piot, Q.-S. Shu, R.
Walker, B. Yunn
Addenda/Errata to Previous Minutes
None.
Items of Discussion
C. Bohn presented the latest shift schedule for discussion, with
emphasis on the rationale for the next two weeks. The two-week scheduling
boards are in preparation and will be ready imminently in the FEL Facility
Break Room. (Note: As of this writing, one has already been prepared.)
They will be used to indicate shift tasks, and will be maintained and updated
weekly. Some discussion ensued about the need to keep people informed of
the specific tasks attendant to their shifts. Plans are to do this not
only by way of the aforementioned boards, but also via e-mail. R. Walker
was slated to e-mail FEL shift plans today. The desire is to handle
scheduling matters in the same way as is done for CEBAF, although there are
complications in that the FEL is now just entering commissioning, whereas
CEBAF is operating. Nonetheless, we will try.
R. Legg and C. Bohn presented this week's injector commissioning
highlights:
- Electron beam, generated with the drive laser, was propagated at 350 keV
through the buncher cavity and into the viewer immediately preceding the
cryounit. This was done with the buncher powered at various levels ranging
from 0-2 kW. PARMELA settings thus far seem to work fine. The vacuum leak
at the light box has improved with time, with the latest readings at
7x10^-11 torr. However, the vacuum is observed to degrade when the buncher
is powered, for example reaching 4x10^-9 torr when the buncher is at 2 kW.
The buncher needs rf processing to reduce outgassing, and this will be
scheduled. Legg will develop a rough estimate of the frequency for
recharging the photocathode in view of these considerations.
- The exit cavity of the cryounit was operated to about 9.5 MV/m, at which
the IR interlock triggered.
- During swing shift on 29 Oct 97 a vacuum fault impeded srf commissioning
of the FEL cryounit. It limited cavity performance to 3 MV/m, and several
hours of remedial rf processing failed to improve performance
significantly. Subsequent investigation of the cause the next morning
revealed that the helical-flex vacuum seal for the warm window was bad.
The window itself appears to be undamaged. The cryounit requires thermal
recycling to remove the air, and it has already been warmed up. Plans are
to replace the faulty seal, cool down Tuesday, 4 Nov 97, and resume srf
commissioning. The net effect of this development is a one-week delay in
commissioning the injector.
R. Legg discussed the procedure for setting up the straight-ahead
dump. A 7cm x 7cm spot is required at the dump face to avoid melting it,
and it is generated by rastering the beam. He calculated that, given
a 1.1 mA, 2.4-mm-radius beam, the time to melt the dump face was 30 ms,
representing the worst-case scenario. Therefore, the FSD interface for the
raster should be required to respond in less than 3 ms. The FSD system can,
in fact, respond much faster, but the trouble occurs in designing a circuit
to decide if the AC power to the magnet is just going through the zero
crossing or has failed. This is programmed in K. Jordan's I&C package. A
second issue is inductive heating of the vacuum pipe. He mentioned we
might want to insert a ceramic break in the dump line with correctors
mounted over the break. It might be necessary to use an aluminum chamber.
Legg will contact Chen in Hall C for input on these matters.
It was noted in subsequent discussion that the air-core correctors
for the dump line (and for the linac in general) may not be available at
the time we will be ready to take tune-up beam to this dump. Consequently,
G. Biallas will check to see if spare CEBAF air cores are available, and Bohn
will ask D. Douglas to assess whether CEBAF air cores would suffice for
commissioning with tune-up beam. These tasks are necessary to enhance our
confidence in being able to take tune-up beam to the straight-ahead dump
before Christmas to get ready for preparing polarized targets for the GEN
experiment. (Aside: J. Boyce remarked that he thought the target chamber
would not be ready for installation until January, but he will check and
report next week on this as well as electron-beam requirements for target
production.)
Piot reported that the quad-scan emittance software is complete and
ready for testing. He needs the model server, but has no information on its
availability date. Bohn will contact S. Witherspoon for information.
New Issues
None.
New Action Items
- FEL Commissioning Team: Enjoy ARM training. (4-5 Nov 97)
- Legg: Develop rough estimate of the frequency for recharging the
photocathode in light of recent vacuum measurements. (due 7 Nov 97)
- Walker: Ensure rf processing of the buncher cavity is scheduled at the
daily 1145 scheduling meeting.
- Walker: E-mail two-month shift schedule on 31 Oct 97. E-mail updates
as they arise. (done 31 Oct 97, appropriate follow-up needed)
- Walker/Legg/Bohn: Assign tasks to the November shifts. Post
shifts/tasks on the FEL Facility Break Room white boards. E-mail the
information to affected (infected?) individuals. (due 4 Nov 97 -- next
week's tasks are already posted on one of the white boards)
- Bohn: Find out date of availability of model server. (due 4 Nov 97)
- Legg: Resolve issue of inductive heating of straight-ahead dump line.
(due 7 Nov 97)
- Biallas: Check on availability of spare CEBAF air-core correctors.
- Douglas: Assess utility of spare CEBAF air-core correctors with tune-up
beam to the straight-ahead dump.
Old Action Items
- Bohn: Work with M7 to identify system owners and their
responsibilities, maintenance provisions, and escalation policy. (due 7 Nov
97) [Note: Much was accomplished this week toward completion of this
action, but it was not reported at today's meeting. M7 has tasked Bohn to
draft a detailed list of maintenance group leaders for the various FEL
systems. Once complete, Bohn will brief the FEL Commissioning Team.]
- Piot: Estimate resource requirements for developing software for
automating acquisition of phase-space-tomographic maps. (due 27 Oct 97)
[Note: Task complete, except Bohn needs to follow up with J. Song to
ascertain his work load. Will do by 4 Nov 97.]
- Bohn: Work with M7 to establish criteria for transferring the FEL as a
user facility to the Operations Department. (due 30 Jan 98)
Procedures in Work
Cryomodule Setup
- Set Cavities to Nominal Gradient Merminga, finalize by 1 Dec 97
First Light Setup
- Thread to Straight-Ahead Dump Douglas, 1 Dec 97
- Dump Setup Legg, finalize by 1
Emittance Growth from CSR
- Tomographic Phase-Space Map Piot, 1 Dec 97?
- Back Leg Thread Douglas, 1 Dec 97
Thread Beam around Machine, Top-Level Douglas, 1 Dec 97