Next Meeting

Date: 11 Mar 99

Time: 1500-1600

Place: FEL Facility Break Room

Agenda for Next Meeting

• Status of spare electrodes (Siggins, 10 min).
• Status of ion-implantation studies (Phillips, Biallas, 15 min).
• Status of focused cesiator (Biallas, 15 min).

This Week's Attendees

G. Biallas, C. Bohn, K. Jordan, L. Phillips, T. Siggins, C. Sinclair, R. Walker

Discussion

The gun is in process of being resurrected after an arc Tuesday night. At this writing (1710, 4 Mar 99), it is being high- voltage processed after an 8-hour heat clean and is sitting relatively quiet at 504 kV. The cathode will be made tomorrow morning after a brief heat clean tonight, and hopefully the gun will be back in operation.

The focus of this meeting was on plans for a gun rebuild. There are a few essential facts that guided the discussion and conclusions:

1. A 330 kV gun suffices nicely for the program at hand right now.
2. There is no body of data from which to draw conclusions about the procedure to follow for ion implantation.
3. The focused cesiator is about 2 months away from installation on the gun.
4. No one feels particularly lucky when it comes to the gun; rather, the prevailing attitude is risk-averse.
5. The overarching assumption is that JLab will want to keep the FEL up and running rather than mothball it.

In view of these facts, the following plan was adopted by the attendees:

1. When the gun dies, replace the cathode wafer and do no more. The prognosis for restoring a 330 kV gun with the existing electrodes is very high. Perhaps the change in the deuterium-cleaning apparatus will result in a nice improvement in quantum efficiency; find out by making the cathode and doing a measurement before doing high-voltage processing with the newly installed wafer.
2. Fabricate (~3-5 weeks), test off-line (~1 week), then install and use the new focused cesiator. Keeping cesium off the existing electrodes could be all that is needed for substantially enhancing the achievable post-cesiation voltage. We know that the uncesiated electrodes can be "routinely" taken to 520 kV.
3. Polish the spare ball to 1 micron and have it in ready reserve should item 1 fail.
4. Start well-defined ion-implantation experiments, and possibly DLC experiments, to identify working procedures and polishing requirements. Use the two existing 6-inch disks as test samples, and make more of them. Do not process the spare cathode ball until a reliable procedure is identified.

The issues mentioned in the last meeting minutes concerning the design of the focused cesiator are now all resolved, save for one: the cesiation time scale. There is a factor-of-ten discrepancy between G. Biallas' calculation and C. Sinclair's calculation, and the discrepancy will be resolved off-line.

To get the ion-implantation studies underway, G. Biallas will work through G. Neil to have D. Bullard polish the two existing disks, and he will arrange for the fabrication of more disks. The attendees regarded it to be imperative to establish not only the procedure (implantation/coating versus fineness of polishing), but also experimental technique. There have been no in-house experiments, so there surely is no technique at this time. The attendees likewise considered it imperative to have a meeting with the William & Mary contingent (D. Manos and Ling-Ling) to discuss details of the experimental program, its goals, and the expectation of the participants.

The attendees were unanimous in their agreement that a second experimental gun should be constructed off-line to test the array of ideas that have been arising during the course of the discussions of this Committee. C. Bohn suggested that the matter is of sufficient urgency and interest that it merits dedicating some funds from the FEL Upgrade program. Now is not too early to begin devising a strawman design for an experimental gun.

Closed Action Items

• Biallas: Resolve pointing (hole size) and thermal control issues associated with Phillips' cesiator design. Status: Done, except for uncertainty in the calculation of cesium-deposition rate.

New Action Items

• Biallas/Sinclair: Resolve discrepancy in the calculation of cesium-deposition rate with focused cesiator design. (due 9 Mar 99)
• Biallas: Through G. Neil, arrange for D. Bullard to polish the two existing 6-inch sample electrodes. (due 8 Mar 99)
• Biallas: Arrange for fabrication of additional 6-inch sample electrodes. (due 10 Mar 99)
• Dylla: Arrange a meeting between FEL Gun Committee members and William & Mary staff to define the experimental program for ion implantation and coating electrodes. (due 10 Mar 99)
• Siggins: Polish the spare cathode ball to 1-micron fineness. (due 12 Mar 99)

Old Action Items

1. Sinclair: Prepare procurement package for DLC-coated samples for Dylla's signature. Status: On hold.
2. Siggins/Biallas: Specify design of experiment to measure cathode temperature. (due date TBD)
3. Dylla: Ascertain feasibility of low-cost "load lock" for cathode-processing experiments in the ARC. Status: No progress due to lack of funding. (due date TBD)
4. Fugitt: Follow through with Ling-Ling on having her develop a strawman table of HV experiments on candidate electrode materials. Status: To be discussed in meeting with William & Mary per New Action Items above.
5. Siggins: Begin scanning gun data and, with D. Gilchrist's help, compiling information into an electronic logbook. Status: Web site was created; progress slowed by recent FEL gun and commissioning activities. (due 19 Mar 99)