Minutes of FEL Gun Committee Meeting
Thursday, 10 Dec 98
Recorder: C. Bohn
Next Meeting
- Date: 17 Dec 98
- Time: 1500-1600
- Place: FEL Facility Break Room
Agenda for Next Meeting
Group activity to schedule tasks for planned January wafer change-out.
This Week's Attendees
C. Bohn, J. Fugitt, J. Gubeli, K. Jordan, G. Neil, L. Phillips, T.
Siggins
Discussion
The bulk of the meeting was dedicated to reviewing wafer history data.
T. Siggins presented the data from two successful wafers dating back to
early this year. One was not anodized, and the other was anodized.
Siggins' notation and presentation of the histories was concise, clear,
and well done. He will continue by looking at the histories of other
wafers.
The general trend suggested by the data presented is that high-voltage
processing needs to be done not at ~420 kV, as was done on these early
cathodes with, at best, mixed success, but rather at ~500 kV, as done on
recent cathodes with apparent success. Also, the early histories
reflect inconsistency in the choice of HV-processing voltage; it was
"hunt and peck". The final version of our HV Processing Procedure needs
to rectify this matter and provide guidance on when specifically to stop
ramping up the processing voltage.
The second main topic of discussion was a presentation by J. Gubeli and
K. Jordan concerning the status of the cathode scanner. The software
now permits use of the mouse to decipher quantum efficiency and current
versus position on a given scan pattern. The current has been
calibrated, and the QE is derived from the current. Gubeli and Jordan
are now considering how to set up to do remote scans, i.e., without
having to enter the FEL vault. An interesting observation from scans of
the present wafer: they reflect no evidence of degradation at the
location of the drive-laser spot despite the many hours of cw runs done
with fixed DL spot location. This cathode scanner is good work!
Lastly, the Committee considered a memo on "Near-Term Improvements to
the Present FEL Gun" provided by C. Sinclair, who was unable to attend.
Bohn will have the memo distributed to all Committee members.
Closed Action Items
- Biallas: Distribute documentation of B. Schneider's cathode
temperature calculations to members of Gun Committee.
Status: T. Siggins gave C. Bohn spreadsheets of results. Bohn will
distribute them to members of the Gun Committee.
- Bohn: Distribute compilation of FEL gun FLOGs to members of Gun
Committee.
Status: Done.
- Dylla: Inquire of M7 to determine their willingness to adopt a
load-lock design effort as a formal Division task.
Status: Discussed
with C. Leemann. The funding-induced dearth of designer resources
negates the prospects for any near-term engineering design.
- Biallas: Preposition resources for fleshing out designs of candidate
load locks.
Status: Not possible due to paucity of resources in
Accelerator Division -- see Dylla action above.
New Action Items
Old Action Items
- Siggins/Biallas: Specify design of experiment to measure cathode
temperature. (due 17 Dec 98)
- Dylla: Ascertain feasibility of low-cost "load lock" for
cathode-processing experiments in the
ARC. Status: No progress. (due 10 Dec 98)
- Dylla: Work with contacts in academia to identify graduate-student
candidates for ARC experiments on electrode materials and geometries.
Status: No progress. (due 10 Dec 98)
- Fugitt: Follow through with Ling-Ling on having her develop a
strawman table of HV experiments on candidate electrode materials.
Status: Discussions are now ongoing. (due 10 Dec 98)
- Fugitt: With Siggins and Phillips, begin filling out "wafer history
charts", starting with the most recent wafers. Status: Siggins has
handwritten summaries of the histories of the last two cathodes that he
presented this meeting. The remaining histories still need
compilation. (due 17 Dec 98)
- Siggins: Begin scanning gun data and, with D. Gilchrist's help,
compiling information into an electronic logbook. Status: Siggins will
talk to L. Wells about getting "scanning support". (due 17 Dec 98)
- Jordan: Quantify cathode scans, being careful to ensure the scanner
intensity does not drive the physics into the Child-Langmuir regime.
Status: Done -- see "Discussion" above