Next Meeting

Date: 14 Jan 99

Time: 1500-1600

Place: FEL Facility Break Room

Agenda for Next Meeting

C. Sinclair's presentation on ideas for a load lock.

This Week's Attendees

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

Discussion

The principal purpose of this meeting was to scrutinize the plan for rebuilding the cesiator and changing out the cathode wafer in the FEL gun. G. Biallas presented the current version of the plan, and the Committee adopted it with a few recommendations/revisions:

• Install the best available wafer; J. Gubeli will do a visual screening of existing wafers.
• Mask the wafer prior to installation; do not anodize it.
• Mount and deuterium-clean the wafer this week in parallel with baking the cesiator.

Regarding detailed procedures for high-voltage processing and heat-cleaning the wafer after installation, the most likely course of action will be to HV process to 420 kV, then heat clean for 20 hours at 600 C. T. Siggins advised that this sequence had always worked prior to the arc event that damaged the electrode(s). Hopefully our round of HV processing to 510 kV smoothed the damage site(s) so the "old" procedure will work. If not, we will go back to 510 kV on the new cathode. The prime motivation is to inhibit arc-induced degradation of quantum efficiency during HV processing. Sinclair feels, based on calculations of back-streaming ions, that this mechanism is a dubious one for degrading QE, meaning that going to 510 kV would not matter. But the general feeling is to stick with a procedure "known to work" and hope it works again. We can revisit this "decision" later, if need be. Regardless, K. Jordan will make provisions for datalogging the cathode thermocouple reading and the mass-4 partial pressure during the heat-clean cycle with the hope that this information might contribute toward eventually formulating a "final" procedure.

L. Phillips will check to see if there is a surface profilometer available for looking at "speckled" wafers. The plan is to take a surface profile of what Gubeli determines to be the worst wafer.

Sinclair mentioned that he has a vendor that can inexpensively deposit diamond-like carbon (DLC) coatings on large samples. These coatings are amorphous, not crystalline, and Sinclair found in past studies that they are capable of holding off fields of order 40 MV/m without field-emitting. There are some caveats, e.g., the cited data is in the absence of significant cesium abundance, but he potential surely merits further experiments with, for example, Venhaus' apparatus. C. Bohn said he would bring the matter to F. Dylla's attention (which he did immediately after the meeting -- Fred will get with Charlie).

Closed Action Items

• Fugitt: With Siggins and Phillips, begin filling out "wafer history charts", starting with the most recent wafers. Status: History exhibits a demarkation coinciding with the arc event that damaged the electrode(s), as remarked in the discussion above. It is therefore unclear how much aid further compilation would bring.
• Dylla: Work with contacts in academia to identify graduate-student candidates for ARC experiments on electrode materials and geometries. Status: Tabled -- W&M will fully support Ling-Ling; other possibilities will be explored informally as time passes. (due 10 Dec 98)

New Action Items

• Biallas: Produce final version of wafer change-out schedule and post in the FEL Facility. (due 5 Jan 99)
• Phillips: Assess availability of profilometer. (due 6 Jan 99)
• Dylla: Meet with Sinclair regarding procurement of DLC-coated samples. (due 8 Jan 99)

Old Action Items

• Siggins/Biallas: Specify design of experiment to measure cathode temperature. Status: No progress. (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 are continuing; see above comments on DLC coatings. L. Phillips may choose to get involved, as well. (due 22 Jan 99)
• Siggins: Begin scanning gun data and, with D. Gilchrist's help, compiling information into an electronic logbook. Status: No known progress since last meeting. Bohn advised Siggins that K. Hanafan is capable of helping. (due 15 Jan 99)