Next Meeting

Date: 4 Feb 99 (two weeks later, not one week)

Time: 1500-1600

Place: FEL Facility Break Room

Agenda for Next Meeting

• Discuss outcome of procedure for bringing up the gun (Siggins, 15 min).
• Check status of ion-implantation studies (Phillips, Biallas, 15 min).
• Discuss progress on focused cesiator design (Biallas, 15 min).

This Week's Attendees

G. Biallas, C. Bohn, J. Gubeli, K. Jordan, G. Neil, L. Phillips, T. Siggins

Discussion

The gun is ready for high-voltage processing, etc., which is slated for early next week. The metal splatter on the last cathode was aluminum, with 99% certainty, according to Carol Kaliel. Thus, the principal concern at this point is whether there is aluminum splattered on the electrodes that will field-emit after exposure to cesium. We took the electrodes to 510 kV prior to opening the gun, but of course we did not check the performance after cesiation. The plan is to:

1. Process the gun to 430 kV (20% over the operating voltage, which should be sufficient based on past experience).
2. Heat clean at 600 C. Monitor the mass-4 peak via software built into the RGA; upon passing through maximum amplitude, turn off the heater and let cool to ambient temperature.
3. Cesiate and make the cathode. Do a quantum-efficiency scan.
4. Run the gun to 360 kV with the conditioning resistor in place.
5. Run the gun to 350 kV with the running resistor in place.
6. Verify 60 pC at 350 kV.

Concerning the aluminum splatter, its source is uncertain. Perhaps it is the low-impedance beam shield at the cesiator, though there is some question about the composition of the shield. Unfortunately one cannot inspect the shield remotely for pits. Regardless, the composition of the splatter is different from previous episodes, and presumably the cause is also different. The question merits further thought.

G. Biallas talked about cost-benefit of various gun-improvement options. Given that we cannot afford a load lock, we deferred discussion of that option. The most promising low-cost plan of attack appears to be identifying a more field-emission-resistant electrode material, make electrodes from it, and in the process modify the lip of the ball for lower surface field. Another promising option appears to be constructing and installing a focused, self-heat-cleaning cesiator. Consequently, G. Niel will ask D. Bullard to get some 6-inch plates fabricated and polished, and in parallel teach the W&M graduate student (Ling-Ling) how to polish. When the samples are available, first thing to try will be nitrogen-implantation since it involves no coating, and therefore no potential flaking. Ling-Ling will measure voltage-standoff capability using Venhaus' apparatus (the start of her dissertation work), and hopefully we will have some data in the foreseeable future. G. Biallas will compose a drawing of the new cesiator (second priority to his injector-owner commissioning tasks).

Closed Action Items

• Biallas: Update list of incremental upgrades and their respective payoffs, and e-mail the list to Committee members. Status: Done, and revised list was presented at today's meeting.

New Action Items

• Siggins: Identify possible sources of aluminum splatter in the gun.
• Niel: Ask D. Bullard to get some 6-inch plates fabricated and polished, and in parallel teach Ling-Ling how to polish. (due 28 Jan 99)
• Biallas: Compose a strawman drawing of the new cesiator. (due 4 Feb 99)

Old Action Items

• Sinclair: Prepare procurement package for DLC-coated samples for Dylla's signature. Status: Unknown. (due 4 Feb 99)
• Siggins/Biallas: Specify design of experiment to measure cathode temperature. (due date TBD)
• 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)
• Fugitt: Follow through with Ling-Ling on having her develop a strawman table of HV experiments on candidate electrode materials. Status: Discussions still ongoing, and will probably accelerate in view of plans discussed above. (due 4 Feb 99)
• Siggins: Begin scanning gun data and, with D. Gilchrist's help, compiling information into an electronic logbook. Status: Web site was just created; progress should commence. (due 4 Feb 99)