Next Meeting

None. This was the final meeting of the Committee.

Agenda for Next Meeting

Not Applicable.

This Week's Attendees

G. Biallas, C. Bohn, F. Dylla, K. Jordan, T. Siggins, C. Sinclair

Closed Action Items

• Sinclair: Prepare procurement package for DLC-coated samples for Dylla's signature. Status: Complete. Implementation awaits availability of sample plates.
• Siggins/Biallas: Specify design of experiment to measure cathode temperature. Status: Shelved. Sinclair pointed out that Jefferson Lab produces GaAs wafers with the best surface-escape probabilities available anywhere, so precise quantification of cathode temperature is probably less important than other ongoing gun-related activities. He did note, however, that the experiment would still be nice to do since there isn't a comprehensive data base available. But given our limited resources, it has relatively low priority.

New Action Items

• Bohn: Prepare closeout memo to F. Dylla on behalf of the FEL Gun Committee.
• Jordan: Procure and install greenie laser for measuring/monitoring cathode QE.
• Biallas: Rectify (reverse) the nitrogen flow in the gun that prevails during heat cleaning.
• Siggins: Check fit-up of parts for apertured cesiator in preparation for welding.

Discussion

Compared to recent history, the FEL gun is working exceptionally well. Though poorly quantified, the QE at the start of this run must have been somewhere between 1-5%, and it is still high. Possibly the gun will not need recesiation at any time during the present one-month run -- we'll see. It turns out that the previous cathode ball had been stress-relieved by baking for 8 hours at 550 C, whereas the replacement ball (in use now) was not. A bake softens the stainless steel, but it is unclear physically what causes the difference in field-emission performance. Again, there is insufficient data by which to draw a conclusion -- it could just be statistical, i.e., luck of the draw. The present ball still emits dark current, which is principally why we are operating it at 320 kV rather than at higher voltage. And it has yet to be recycled (the usual HV processing, heat clean, and recesiation), so there is no data yet concerning its "availability". Nonetheless, thus far the gun's performance is remarkably good.

T. Siggins discussed difficulties with measuring and monitoring the cathode's QE versus time. Adding a greenie laser should solve the problem, and F. Dylla asked K. Jordan to procure and install one. Moreover, there is a need to reverse the flow of nitrogen to get rid of streaming during heat clean and hopefully prevent formation of the low-QE spot at the center of the cathode wafer. G. Biallas will rectify that.

G. Biallas reported that all internal parts are complete for the apertured cesiator, and all detail drawings are complete. The internal parts are not yet welded, and there are external parts still out for bid (specifically, the thermal isolator for the valve, and the support for the tube). Before welding is done, fit-up of the parts needs to be checked. Siggins will check fit-up. In addition, the mockup of the cesiator has been tested. A current of 29 A establishes a 250 C temperature of the tube that will contain the cesium vapor, an acceptable result.

Biallas reported that L. Phillips has asked that a stand-alone tube and cross be provided for the preinstallation tests of the cesiator given that his bell jar is "inconveniently" located in a clean area. C. Sinclair still plans to contribute the thickness monitor for the tests.

Not much progress has been made toward the ion-implantation studies. Siggins and D. Bullard are still polishing sample plates. Siggins estimates the first sample plates (at 9 µm finish) will be passed to W&M in about one month. First measurements will probably be available in about three months. Bohn reaffirmed that the apertured cesiator still takes priority over the ion-implantation studies, but the latter effort is nonetheless an important one given its potential payoff. As an aside, Biallas has given several cubic-cm-sized samples of the plate material to W&M (Lingling) for auger analysis with the hope of identifying the composition of the irregularities that have been surfacing during the polishing effort.

For the most part, this Committee has met its November 1998 charge. Most importantly, a clear priority and pattern for incrementally upgrading the FEL gun has presented itself during the course of the Committee's discussions. Therefore, it is now time to convert to a design effort in the manner of a subtask of the Injector WBS for the FEL Upgrade. C. Bohn will prepare a final report from the Committee to F. Dylla that will answer the original charge and itemize topics to be considered as part of the design effort. The source of the latter will be the set of meeting minutes. Bohn will coordinate the document with Committee members prior to finalizing it. Leadership of the design effort remains to be established.