Minutes of Impromptu FEL Gun Committee Meeting

Friday, 5 Feb 99
Recorder: C. Bohn

Next Meeting


Date: 11 Feb 99
Time: 1500-1600
Place: FEL Facility Break Room

Agenda for Next Meeting


This Week's Attendees


G. Biallas, C. Bohn, F. Dylla, J. Gubeli, K. Jordan, G. Neil, T. Siggins, C. Sinclair, R. Walker, plus several interested observers.

Discussion


Due to the present problem resurrecting the FEL gun (for details, see this week's FEL report), C. Bohn called an impromptu meeting of readily available FEL Gun Committee members and interested (innocent?) bystanders. The problem decomposes into two facets -- poor quantum efficiency, and inability to hold voltage after cesiation.

A number of options were delineated, and they fell into the following categories: higher-voltage processing, dry-nitrogen processing, replacing the electrodes with improved electrodes, testing to localize the source of cathode contamination, and building a "directed cesiator". In-depth discussion was limited to options that are viable (cheap!) candidates for immediate or near-term implementation.

The following top-level plan ensued:

  1. High-voltage process to the highest achievable level (~575 kV), then do a long heat clean, recesiate, and try again to turn on the gun. (Principal: Siggins)

  2. If (1) is unsuccessful, try processing with ~10-6 Torr dry nitrogen, then repeat (1); C. Sinclair advised that SLAC has found success with this technique. (Principal: Dylla)

  3. Modify the lip (peak-voltage region) on the spare ball in parallel with (1) and (2). (Principal: Biallas)

  4. Replace the cathode ball with the modified spare ball. (Principal: Siggins)

  5. Start the ion-implantation experiments now, with the goal of developing a field-emission- resistant anode plate for perhaps the next gun rework. (Principal: Phillips, with aid from Siggins)

  6. After the next installation of a new wafer and baking the gun, cesiate the cathode and measure its photoresponse prior to high-voltage processing. If it is poor, we then know there is something wrong with the deuterium-cleaning procedure (or some other off-line process). If it is good, we know there is something going on with high-voltage processing that is contaminating the cathode. (Principal: Siggins)

  7. Build a stalk and cesiator that permit cesiating the cathode in the retracted position, thereby mitigating deposition of cesium on the outer surface of the ball. This will cost a few k$, and F. Dylla approved the expense. (Principal: Biallas, with aid from Sinclair and Siggins)