Next Meeting
Agenda for Next Meeting
Item Person Responsible Time ---- ------------------ -------- Status of Open Action Items All 5 min Status of Gun Biallas 15 min Status of Commissioning Bohn 10 min Commissioning Schedule Bohn 10 min New Issues All 5 min
This Week's Attendees
J. Bennett, S. Benson, G. Biallas, J. Bisognano, C. Bohn, J. Boyce, D. Douglas, F. Dylla, J. Fugitt, E. Gillman, A. Hofler, C. Hovater, K. Jordan, P. Michel, D. Oepts, P. Piot, M. Shinn, T. Siggins, R. Walker, B. Yunn
Closed Action Items
Items of Discussion
C. Bohn introduced Dr. Peter Michel who arrived from Rossendorf Laboratory, Dresden, Germany, on a three-month sabbatical to work with us. Michel is responsible for the electron-beam diagnostics for Rossendorf's superconducting FEL that is now under construction, so he will focus on diagnostics and gain experience with machine operations during his stay. Also, P. Piot has returned from France, and we are all very pleased to have him back.
High-voltage processing of the gun at 420 kV was completed over the weekend. The cathode was heat-treated Monday and, after cooldown, was cesiated Tuesday afternoon. Unfortunately, and surprisingly, two problems subsequently arose. First, the photoresponse of the cathode after cesiation was very poor. Second, field emission down the beamline showed up at around 300 kV. A plan to diagnose the problems was formulated Wednesday and implemented yesterday. The outcome is that, with high probability, the source of field emission is on the front of the cathode ball but not located on the cathode wafer itself. This finding was ultimately established by retracting the cathode and discovering the same field-emission spot at the same location and roughly the same voltage. PARMELA calculations by B. Yunn, facilitated by H. Liu, affirmed the front of the ball is visible on the ceramic viewer at the solenoid settings that were in place during the observations. During the process of diagnosis, the cathode was observed to have "nonexistent" quantum efficiency (QE); observable electron beam could not be extracted from the cathode even when it was subjected to full pulsed-power drive-laser light. There was a small vacuum leak during a portion of the bake, and one conjecture is that the wafer oxidized as a result of the leak. If so, it will need to be replaced, but presently there is insufficient data to establish a conclusion concerning the bad QE.
Right after today's Commissioning Meeting, most of the attendees stayed to formulate immediate plans for gun work. The resultant plan is as follows:
If the gun does not work Monday afternoon, then:
At this writing (1120 Friday, 25 Sep 98), the planned work is in progress.
C. Hovater discussed the electronics for the beam-current-monitor cavities. As they are currently configured, the output signal comes from a phase detector that swings between ±90 deg. The signal is insensitive to differences in the bunch length between the forward and recirculated beams. A diode can be added, if desired, to measure power, so it is possible to extract both amplitude and phase from the devices. It would be helpful to do so, and Bohn will get with G. Krafft off-line to generate signal requirements for Hovater. Adding the diode would take about three man-days to complete.
K. Jordan presented an update on the status of the FEL's Machine Protection System (MPS). A detailed checkout of the MPS ensued this week, with the principals being J. Coleman, R. Walker, and K. Jordan. The essential findings thus far are: all MPS hardware is now operational; however, user-friendly screens are generally lacking, with many indicating "invalid beam mode" without pointing to the specific cause. The Safety Systems Group needs to fix the screens by labelling the various channels. Signed-off certification of the MPS should occur today. MPS documentation still needs to be completed; Walker is assisting Jordan and the Safety Systems Group in doing so. One detail that was discussed concerned the dump-line quadrupole magnets; current limits from these magnets will not be inputs to the MPS because there is already a redundancy of protection for the dumps (vacuum, water temperature, and water flow), and the quads will need to be adjusted as beam parameters, e.g., energy, are changed.
Considerable discussion followed concerning where to locate the FEL Bugger Log, especially since the MPS checkout revealed the Log entries were incomplete. Following the practice of the Operations Department (which is what we will continue to do!), the Log has been kept in the MCC Control Room. At this moment it is in the FEL Control Room since MPS checkout has been occurring there, and the gun experiments (that were run from the FEL Control Room) had required some buggers. Once commissioning resumes, plans are that the Bugger Log will again be placed in the MCC Control Room. It can be kept up to date without undue hassle simply by phoning the MCC and asking that the appropriate log entries be made. Bohn will deviate from this plan only if R. Lauze advises him to do so.
New Issues
See discussion above.
New Action Items
Old Action Items
Procedures in Work
Procedures Needed for Recirculation
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