Next Meeting
Agenda for Next Meeting
Item Person Responsible Time ---- ------------------ -------- Status of Open Action Items All 5 min Status of Commissioning Bohn 20 min Commissioning Schedule Bohn 10 min New Issues All 5 min
This Week's Attendees
J. Bennett, S. Benson, G. Biallas, C. Bohn, J. Boyce, R. Campisi, D. Douglas, F. Dylla, R. Evans, E. Gillman, A. Grippo, K. Jordan, G. Krafft, R. Lauze, L. Merminga, P. Michel, D. Oepts, P. Piot, C. Rode, M. Shinn, T. Siggins, R. Walker, B. Yunn
Closed Action Items
New Action Items
None.
Old Action Items
Items of Discussion
T. Siggins summarized the status of the photocathode gun. The cathode wafer was replaced early this week and verified to yield a photoresponse. The vacuum bake was readied and executed; tear-down of the bake is slated for this afternoon. The whole process has thus far progressed well. F. Dylla said the last wafer is undergoing a barrage of surface studies at William & Mary which thus far has yielded no surprises.
Plans are to do careful high-voltage processing of the gun, to be supervised by Siggins, starting Monday morning and ending Wednesday morning, followed by heat cleaning the cathode wafer, and then cesiating it after it has cooled down. We should be able to pull electron beam off of the gun starting Thursday morning, 22 Oct 98.
C. Bohn announced that, in view of these developments, the machine will be "frozen" as of noon Wednesday, meaning no further software or hardware upgrades would be permitted prior to resumption of commissioning. The reason is that an audit of the MPS is scheduled for Wednesday afternoon, and Bohn wants to preserve the integrity of the audit.
The two-week commissioning schedule was discussed; plans and philosophy remained unchanged. Please consult the scheduling board and/or the www posting thereof to stay abreast of shift assignments.
F. Dylla mentioned that the FEL budget remains excruciatingly tight, with no significant funds available for procurements. This brings up some questions to be worked off-line, such as how and when to upgrade the gun for better availability.
L. Merminga presented the status of efforts to organize a set of beam-breakup experiments on the FEL. The fundamental motivation is to validate the code TDBBU that calculates BBU in a recirculating accelerator. Once benchmarked, the code can be used with more confidence to establish BBU threshold currents in FEL upgrades or alternative designs. It also could be used to establish with more confidence whether HOM couplers are required on the 7-cell cavities envisioned for the 12 GeV upgrade of CEBAF. Considerable money and effort would be saved were the answer to be "No".
TDBBU predicts the threshold current in the IR Demo to be 27 mA, well below its attainable current. Thus, the strategy is to force the BBU instability in the FEL by, for example, driving the dominant deflecting mode with an external rf source and possibly lowering the electron-beam energy. Stripline kicker and pickup cavities are envisioned. Those used in Nick Sereno's experiment have been found and examined. Their apertures don't match those of the FEL vacuum chambers, so new designs are presently under consideration. B. Yunn pinpointed the optimal locations of the kickers; they will go in the injection line (one horizontal and one vertical). There is an issue concerning the lowest attainable electron-beam energy, particularly if it involves lowering the energy of the injected beam since the "injector aperture" is presently undetermined.
A final plan is anticipated to be available by 15 Nov 98. If the plan were implemented, the BBU experiments would likely be conducted next summer.
G. Krafft reported about further developments in the "stent irradiation program" for Duke. As it stands now, Duke would build the holders to mount the stents on the straight-ahead dump line, and Jefferson Laboratory would build the target and shielding. The purpose of the target is to generate g-rays from the (nominally 2 kW) electron beam; the g-rays serve as the radiation for the stents.
New Issues
None.
Procedures in Work
Unfinished Subsidiary Tasks for Phase Space Metaprocedure
Task Principal
---- ---------
I. Stabilize Drifts in Drive-Laser RF Phase Walker/Fugitt
II. Calibrate RF Gradients
A. Buncher Yunn
B. Cryounit Cavities (fix control screen) Merminga/Krafft/Yunn
C. Cryomodule Cavities Merminga/Krafft/Yunn
III. Reconcile Methods for Setting RF Phase Merminga/Krafft/Yunn
A. Buncher Cavities
2. Minimum bunch length/time of flight
B. Cryounit Cavities
1. Transient phasing
2. Cresting
3. Time of flight
IX. Complete Diagnostics Procedures and Users' Guide Krafft/Piot
A. M_55 #1, #2
B. Happek #1, #2
C. BPMs
1. button calibration factors
2. rotated MEDM spike charts
3. difference orbit data acquisition script
D. Multislit #1, #2
E. Quad/Viewer (at Wiggler, after Wiggler)
F. Multimonitor (at Wiggler)
G. SLM/CSR
H. Zero Phasing
I. Momentum Spread (Injector, Linac Pre-Wiggler, Linac Post-Wiggler)
J. Energy
XIV. Laser Turn-On Procedure Benson