Free Electron Laser Commissioning Meeting
Friday, 13 Mar 98
Recorder: C. Bohn
Next Meeting
- Date: 20 Mar 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
Commissioning Progress Bohn/All 15 min
GEN Irradiation Procedure Boyce/Physics 15 min
Microphonics Measurements Merminga 15 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, J. Boyce, R.
Campisi, J. Delayen, D. Douglas, J. Fugitt, A. Hofler, K. Jordan, R. Legg,
L. Merminga, G. Neil, D. Oepts, P. Piot, Q.-S. Shu, R. Walker, B. Yunn
Closed Action Items
- Walker: Obtain Physics Division input and assign Physics personnel to
the GEN target-irradiation shifts. Status: Complete. Each GEN shift
consists of one FEL operator who is qualified as an ARM, and one Physics
Division representative.
- Shinn (with Benson and Jordan): Resolve how to guard against failure of
the drive-laser EO cells. Status: A comparator that monitors gun current
will be used. A jump in current will trip the MPS.
- Legg: Modify Injector Setup Procedure to incorporate nonzero alpha at
the cryounit exit. Status: Done, but procedure needs updating to reflect
the updated cryounit phases (see discussion below).
Items of Discussion
C. Bohn led a discussion to ascertain where we stand with commissioning
preparations. Highlights of the discussion are as follows:
- Plans are to turn on electron beam at swing shift Monday, 16 Mar 98. The
basic task is to get 2 ľA, 38 MeV beam down to the straight-ahead dump as
expeditiously as possible, hopefully by owl shift Thursday, then install
the GEN target chamber Thursday and Friday, then irradiate GEN targets
through Wednesday of next week. In the process, simple procedures for
turning the machine on and off will need to be identified because repeated
accesses to the vault will be required for GEN target insertion/removal.
- Plans are to turn on electron beam at swing shift Monday, 16 Mar 98. The
basic task is to get 2 ľA, 38 MeV beam down to the straight-ahead dump as
expeditiously as possible, hopefully by owl shift Thursday, then install
the GEN target chamber Thursday and Friday, then irradiate GEN targets
through Wednesday of next week. In the process, simple procedures for
turning the machine on and off will need to be identified because repeated
accesses to the vault will be required for GEN target insertion/removal.
- Bakeout of the gun is complete, and high-voltage processing commenced
last night, progressing to 385 kV. Plans are to go to 420 kV tonight and
let the gun set at that voltage for several hours.
- As wiring for the MPS progressed yesterday, problems with integrating
various subsystems arose. They are being worked out with the goal of
completing the MPS before Monday turn on.
- All first-light magnets are now in place except the oval air cores, one
of which goes on each optical chicane. We need to up the priority for
their measurements in the Magnet Test Stand (see "New Action Items" below).
A question arose on how to adjust the current on the straight-ahead raster
magnets to optimize the spot size on the GEN targets. Biallas said this is
done via an expert screen. A follow-on question arose as to how to observe
the spot at the target location given that the drift between the rasters
and the last viewer is now only about 10 cm. Two options are available,
the first being to move the rasters back for GEN irradiation, and the
second being to install a scintillator in the GEN target chamber. J.
Fugitt will work with people to resolve the issue (see "New Action Items"
below).
- Some vacuum valves are jimmied closed, but Parkinson Inc., will undo them
before turn-on. Bohn needs to check with Parkinson about reactivating the
NEG in the energy-recovery dump line.
- The operator page (viewer images) and save/restore file (theory) are
incomplete. B. Yunn said he discovered an inconsistency with how PARMELA
establishes cavity phases. In particular, the second cryounit cavity phase
needs to be changed from -15 deg to -19.7 deg (Legg will update injector
procedures and save/restore accordingly). Yunn is in process of checking
PARMELA's cryomodule phases before finalizing the output beam from the
cryomodule. D. Douglas awaits handoff from Yunn so he can calculate the
post-cryomodule 60 pC settings and beam dynamics. Once done, Bohn,
Biallas, Douglas, and Yunn will ensure the operator page and initial
save/restore file are complete. Bohn highlighted the urgency of completing
this task quickly.
- Benson is working toward simplifying control of the drive-laser attenuator.
R. Campisi presented results from an extensive set of higher-order-mode
measurements in the cryomodule cavities. Many more resonances are present
than in the conventional CEBAF setup, and one question was whether
cross-coupling between cavities was the cause. The data suggest that
cross-coupling is weak, at the 80 dB level. Rather, the lesson seems to be
that a small change in geometry can lead to considerable change in Q of
strong modes and large change in Q of weak modes. For example, the strong
1890 MHz mode has Q~10^5, about ten times larger than in the original CEBAF
test cavities, and the weak 1730 MHz mode has Q~10^7, about 1000 times
larger than in the original test cavities. For the cryomodule itself, the
beam-breakup-threshold current is about 60 mA assuming a somewhat
pessimistic frequency distribution in the eight constituent cavities.
J. Boyce asked that all FEL WBS managers and integrators attempt to log
on to the www-based ARR system.
New Issues
No new issues sprung forth at the meeting other than those described above.
However, subsequent to the meeting, an uncertainty arose as to the
timeline required for GEN target irradiation. We originally planned for
4-hour runs with 2 ľA current. When we began to develop shift plans, our
Physics Division contacts recalculated the time per target to be 8 hours.
Today, they think it might be as long as 15 hours, presumably due to
inserting round targets in a rectangular raster pattern. J. Boyce will
continue working with Physics Division people to solidify the plans.
New Action Items
- Douglas: Update spreadsheet code to reflect "song-sheet" nomenclature.
(due 16 Mar 98)
- Douglas/Karn: Ready the oval first-light air core correctors for
installation. (due 20 Mar 98)
- Fugitt/Physics: Resolve how to verify spot size on the GEN targets.
(due 20 Mar 98)
- Bohn: Check with Parkinson about reactivating the NEG in the
energy-recovery dump line. (due 13 Mar 98)
- Boyce: Resolve with Physics Division people the time needed to
irradiate each GEN target, and arrange for one of them to give an overview
of the irradiation procedure at next week's meeting. (due 19 Mar 98)
- FEL WBS Managers/Integrators: Attempt log-on to www-based ARR system.
(due 20 Mar 98)
Old Action Items
- Bohn: Test www logbook and shift-summary entries via a trial shift log.
(due 16 Mar 98)
- Yunn/Jordan: Prepare, label, and post to the "FEL operator page" viewer
images of PARMELA beam for the optimized 60 pC setup. Status: Viewer
images for the injection line and injector dump line are posted. Yunn
needs to confirm cryomodule phases in PARMELA, then send to Jordan the
viewer images in the linac up to the wiggler location. (due 13 Mar 98)
- Li: Explore implications of 60 pC settings for CSR experiments.
Status: Li is in process of optimizing the simulation code for faster
execution. Presently, it runs too slow to simulate the first recirculation
arc. (due 20 Mar 98)
- Jordan: Prepare procedure "MPS/BLM Checkout for First Light". Status:
Awaits completion of the MPS. (due 20 Mar 98)
- Yunn/Jordan: Prepare, label, and post to the "FEL operator page" viewer
images of zero-current PARMELA beam given the optimized 60 pC setup.
Status: Status: Viewer images for the injection line and injector dump
line are in process of being posted. Yunn needs to confirm cryomodule
phases in PARMELA, then send to Jordan the viewer images in the linac up to
the wiggler location. (due 13 Mar 98)
- Douglas: Update spreadsheet code to propagate zero-current beam to the
straight-ahead dump given the 60 pC PARMELA settings. Status: Awaiting
handoff of output beam at cryomodule exit from Yunn. (due 13 Mar 98)
Procedures in Work
Emittance Growth from CSR
- Tomographic Phase-Space Map Piot, 15 May 98
- Back Leg Thread Douglas, 6 Mar 98
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 Jordan, 20 Mar 98
(Note: The highest-priority item here is the procedure for MPS/BLM
Checkout for First Light!)