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
- Discuss outcome of procedure for bringing up the gun (Siggins, 15 min).
- Check status of modified spare cathode ball (Biallas, 5 min).
- Check status of ion-implantation studies (Phillips, 15 min).
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:
- 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)
- 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)
- Modify the lip (peak-voltage region) on the spare ball in parallel
with (1) and (2). (Principal: Biallas)
- Replace the cathode ball with the modified spare ball. (Principal:
Siggins)
- 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)
- 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)
- 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)