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:
- Finish alignment checkout (results of which are discussed above),
- Codify the existing collection of 3D PARMELA runs, of which there is an
extensive set of "9,11 MV/m" runs,
- 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
- CATERs need to be followed up when they lack timely completion. Bohn
will need to take the lead here. We will likely do better as we go into
routine commissioning.
- Do we need orbit lock? This depends on stability of the electron beam.
S. Benson pointed out that to date no FEL has used orbit lock. The plan is
to take a shift's worth of data at 1.1 mA when we get to that point and
monitor stability over a several-hour time frame.
- Should we have a PTUNE program available for rf control? L. Merminga
will discuss with L. Doolittle and report back with recommendations.
- When do we formally implement the commissioning infrastructure,
specifically the establishment of an FEL Experiment Coordinator? Bohn
intimated that he was presently unsure and would further cogitate on the
question.
New Action Items
- Bohn: Meet with S. Suhring to discuss procedures for CATER follow-ups.
(due 23 Jan 98)
- Merminga: Meet with L. Doolittle to decipher whether we need PTUNE.
(due 30 Jan 98)
- Bohn/Walker: Review and distribute 3-month shift schedule. (due 20 Jan
98)
- Bohn: Decide when formally to implement the position of FEL Experiment
Coordinator. (due 23 Jan 98)
- Biallas: Install the generic field maps for the QB and QG quads, and
recheck to ensure all magnet field maps necessary for first-light operation
are accessible from the control room. (due 23 Jan 98)
- Bohn: Inform D. Windmueller about FEL SWIS requirements. (due 22 Jan 98)
Old Action Items
- Legg : Develop strategy for optimizing electron beam quality.
(preliminary due 23 Jan 98; final due 30 Jan 98) Status: Held a meeting
on 12 Jan 98 to scope the effort. Results are summarized in the discussion
above. Legg will set up a follow-on meeting once he has codified the
existing PARMELA simulations and after Yunn has returned from Korea.
Procedures in Work
First Light Setup
- CW Setup Legg, finalize 23 Jan 98
Emittance Growth from CSR
- Tomographic Phase-Space Map Piot, 15 May 98
- Back Leg Thread Douglas, 31 Jan 98
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