Minutes of FEL Gun Committee Meeting
Friday, 17 Nov 98
Recorder: C. Bohn
- Date: 24 Nov 98
- Time: 1000-1100
- Place: FEL Facility Break Room
Agenda for Next Meeting
Item Person Responsible Time
---- ------------------ --------
Performance Summary of Recent FEL Cathodes Siggins 15 min
Summary of Standard Gun Procedures Bohn 15 min
Summary of Load Lock Options Biallas 15 min
Discussion All 15 min
This Week's Attendees
G. Biallas, C. Bohn, F. Dylla, J. Fugitt, K. Jordan, G. Neil, L. Phillips,
T. Siggins, C. Sinclair
Closed Action Items
New Action Items
- Dylla: Ascertain feasibility of low-cost "load lock" for
cathode-processing experiments in the ARC. (due 30 Nov 98)
- Dylla: Work with contacts in academia to identify graduate-student
candidates for ARC experiments on electrode materials and geometries. (due
8 Dec 98)
- Fugitt: Follow through with Ling-Ling on having her develop a strawman
table of HV experiments on candidate electrode materials. (due 20 Nov 98)
- Bohn: Meet with Sinclair, then Siggins, to list key processing steps
that will serve as an outline of processing procedures. (due 19 Nov 98)
- Fugitt: With Siggins and Phillips, begin filling out "wafer history
charts", starting with the most recent wafers. (due 8 Dec 98)
- Siggins: Begin scanning gun data and, with D. Gilchrist's help,
compiling information into an electronic logbook. (due 8 Dec 98)
- Biallas: Preposition resources for fleshing out designs of candidate
load locks. (due 24 Nov 98)
- Jordan: Quantify cathode scans, being careful to ensure the scanner
intensity does not drive the physics into the Child-Langmuir regime.
Old Action Items
As Gun Owner, T. Siggins is appointed repository of all FEL gun data and
Items of Discussion
Bohn began by summarizing F. Dylla's charge to the FEL Gun Committee.
He broke the tasks down into two categories, Immediate and Follow-On, the
former relating to the existing gun, and the latter relating to the "next
gun" for the FEL Upgrade. He then emphasized the need to concentrate on
the Immediate Tasks over the next few weeks, and consequently proposed a
schedule that the Committee accepted. Bohn's summary was as follows:
IMMEDIATE TASKS FOR FEL GUN COMMITTEE
- Analyze gun performance from first operation in ITS to now.
- Write standard procedures for maintenance/operation that ensure best
results with the existing hardware.
- Recommend routine measurements to improve reliability using existing and
augmented instrumentation (i.e. RGA, wafer temperature, etc.)
- Investigate and recommend cheap/easy incremental improvements (i.e.,
load lock, arc suppressors on the HVPS, collimated cesium source, etc.).
- Incorporate new procedures and hardware developed by the Polarized
Source Group that could benefit FEL gun operation.
FOLLOW-ON TASKS FOR FEL GUN COMMITTEE
Focus: Recommend best design option and preliminary conceptual design for
the 20 kW Upgrade gun, and estimate its cost, to include:
- Improvements to existing gun (i.e., load lock for cathode processing and
change-out, new electrode materials/geometry, new processing procedures,
- Design of hybrid RF photogun that combines a load lock, the front end of
the Best Technology Gun, and a normal-conducting preacceleration RF cavity.
- New source technologies that could be developed in time for the Upgrade.
One such option is a field emission source based on photo-assisted field
emission from a rugged tip material (ZrC, HfC, LaB6, etc.).
- Specify needed changes in the injection-line hardware.
SCHEDULE FOR IMMEDIATE TASKS
Task Principal* Due Date
----- ---------- -----------
Analyze performance history Fugitt 3 Dec 98
Write standard procedures Bohn 15 Dec 98
Routine measurements Siggins 15 Dec 98
Incremental improvements Biallas 15 Jan 99
Assimilate PSG techniques Sinclair 15 Jan 99
*Each task is a team effort; Principal is expected to solicit input and
Much good discussion followed, the essential outcome of which is
reflected in the list of action items above. Some relevant details that
- Indium soldering of GaAs onto molybdenum is helpful to prevent cracking
of the wafer.
- Only one glass piece is on hand for hydrogen-cleaning wafers; there are
no spares. This is one reason why the Polarized Source Group is reluctant
to let inexperienced people use the H-cleaning apparatus. Getting new
glass pieces is nontrivial, requiring a circuitous route through the Univ.
of Illinois (unless another good glassblower can be found).
- The load lock presently in development by the Polarized Source Group is
intricate, is still being developed, and would take considerable time
(>1 yr) and money to duplicate for the FEL gun. A prerequisite for considering
a load-locked gun like the Polarized Source Group is building is to do some
POISSON studies to see what the field strengths are. One may very well
need considerably different geometry and element sizes to keep the field
strengths below a troublesome level.
- A directional cesiator would likely be a useful near-term option to aid
in mitigating cesium-induced field emission from the electrodes of the FEL
- The FEL, and the Accelerator Division as a whole, needs support from a
team of basic researchers doing high-voltage studies on candidate electrode
materials and coatings. Presently we have only one W&M graduate student
(Ling-Ling); she is in the process of setting up a test stand in the ARC.
It also would be wise to set up Venhaus' apparatus. Bottom line is that at
least one more solid graduate student is needed right now.
Note: Bohn is having these minutes, as well as subsequent minutes, posted
on www under FEL Documentation, Section [10.4.1] -- Photocathode Gun.