Next Meeting
Agenda for Next Meeting
Item Person Responsible Time ---- ------------------ -------- Status of Open Action Items All 5 min Status of Gun/Injector Biallas 15 min Status of Commissioning Bohn/Douglas 15 min Commissioning Schedule Bohn 10 min New Issues All 5 min
This Week's Attendees
S. Benson, G. Biallas, J. Bisognano, C. Bohn, J. Coleman, D. Douglas, F. Dylla, J. Fugitt, E. Gillman, A. Grippo, K. Jordan, G. Krafft, R. Lauze, P. Michel, D. Oepts, P. Piot, C. Rode, T. Siggins, R. Walker, B. Yunn
Closed Action Items
Items of Discussion
R. Li delivered a baby girl on Wednesday, 30 Sep 98, thereby meeting her major FY98 milestone on schedule. The baby's name is Eliza, and she weighed in at 7 lb 4 oz. Everything went according to Rui's calculations.
B. Yunn announced that he now has a PARMELA deck for the entire FEL machine including sextupoles, but that he was unsure about what simulations should be run given that the injected beam has never been characterized fully. D. Douglas pointed out that the original purpose for developing the deck was to ascertain more fully the character of the longitudinal phase space of the beam as it propagates through the machine. For example, less detailed transport simulations indicate that the beam profile at the energy-recovery dump is very sensitive to both the cryomodule gang phase and quadratic nonlinearities in the lattice. It is of interest to explore more carefully, e.g., how to counter the quadratic nonlinearities with the sextupoles and trim quads. C. Bohn reminded everyone that shortly after turn-on, another attempt to use Happek #1 and Multislit #2 will be made, and the attempt will hopefully be facilitated by a newly installed corrector magnet in the injection line. In the meantime, we have a reasonably accurate characterization of the beam in the wiggler region which may be helpful to anchor the code calculations. Douglas and Yunn will put together a plan for the PARMELA simulations.
On Monday the gun's cathode was cesiated after last weekend's heat cleaning. Unfortunately, field emission again showed up at about 300 kV, thereby preventing resumption of commissioning and frustrating everyone involved. Aided by PARMELA simulations combined with observations of the field emission and a careful electrostatic field map of the cathode ball, a diagnosis of the location of the field-emission site was attempted. It was inconclusive. The best guess is that the rim of the hole in the ball in which the cathode is inserted field-emitted with the cathode retracted (inferred from last Friday's observations) due to an accentuated surface electric field, while the cathode itself field-emitted when the cathode was inserted in place (inferred from Monday's observation). We decided to attempt helium-arc processing rather than go directly to opening the gun.
F. Dylla presented an overview of the status of the gun, with emphasis on this week's helium-arc processing. The aim of the helium processing is two-fold -- to smooth out point sources of field emission, and to remove about two monolayers of carbon and oxygen (and whatever else) contaminants from the surface of the electrodes, especially that of the cathode for improved quantum efficiency. The evolution of the arc rate during processing suggests that the processing evolved through two stages, the first being the processing of the cathode ball and anode plate where the field was highest, and the second being the processing of the remaining structures, e.g., the cathode-support stem. The procedure lasted for about five hours, during which an arc current of nominally 50 mA was sustained at a voltage of nominally 500 V. Based on prior studies of helium processing in connection with improving vacuum conditions, the goal was to deposit 0.5 C/cm^2 over the electrodes under these conditions, and the target was nearly achieved by the time the process halted due to running out of helium gas. After processing, the high voltage was ramped up to 420 kV on the cathode. Ramping was slow because its consequence was to blow off a helium monolayer that had been affixed to the electrode surfaces. Blowoff started at the low voltage of 200 kV, resulting in vacuum spikes. The ramp-up took about 16 hours principally because the gun's ion pump was slow at removing helium.
With helium processing and high-voltage ramp-up now complete, the "gun plan" is as follows:
We will know the outcome sometime Monday afternoon. If we can run, we will then resume commissioning per the plans discussed during the last two Commissioning Meetings. Shift assignments for the next two weeks are indicated on the scheduling board.
R. Walker has been working this week with members of the Safety System Group toward certifying the Machine Protection System. Walker indicated that 80-90% of the MPS is now certified, but there is a four-item punch list awaiting resolution. Bohn asked him to complete the certification by noon Monday given the hope of resuming beam operations Monday afternoon, and he got together with J. Coleman immediately after the meeting for this purpose.
G. Krafft advised that the two additional M_56 cavities should be available within 1-2 weeks. They already exist, and the flanges and beam tube of one of them are being reworked to fit in the reinjection (5F) region. The other will be installed near the beginning of the back-leg (4F) region. Bohn and Krafft will work together to time their installation compatibly with the commissioning activities. No software additions are needed for these cavities.
Dylla closed the meeting by announcing that the tentative date for the FEL Facility dedication is 4 Nov 98, a date driven by the availability of DOE Secretary Bill Richardson. The FEL Commissioning Team will do its best to make progress on high-cw-power lasing with energy recovery before then while maintaining a systematic, "configuration-controlled" approach consistent with the "High-Power Setup Procedure". Bohn will do his very best to keep everyone's stress levels down, though he had not been intending to use "gun control" for this purpose! May God be with us. In any event, as Fred said, we have much to be proud of already.
New Issues
None.
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