Management

Highlights: the week was devoted to high-voltage processing and cathode preparation for the gun.

C. Bohn and G. Neil accompanied A. Todd of AES on 1 Feb 99 to Crystal City, VA to visit Dr. Darrell Collier, Chief Scientist of the Army's Space and Missile Systems Command. The Army is exploring alternative programs to be pursued at HELSTF, and expressed interest in possibly duplicating the JLab FEL there, as well as possibly supporting development of an advanced high- average-current injector.

Bohn and Neil then proceeded to Los Angeles, CA to meet with LtCol Randall Weidenheimer of the Air Force's Space and Missile Center as well as a number of Aerospace Corporation staff on 2 Feb 99. The Air Force is embarking on a study of lasers for strategic defense applications, as well as in ancillary roles. Col Weidenheimer is the study director. The study is to include FELs. The Air Force is now planning to sponsor JLab into its supporting contractors on behalf of high- average-power FELs.

Dr. Charlie Brau of Vanderbilt University visited JLab on 4 Feb 99 to discuss the potential use of superconducting rf accelerators in medical x-ray sources. 

Dr. Michael Kelley, chairman of the Laser Processing Consortium, recently left DuPont Research and joined the College of William and Mary as a professor of Applied Science. Michael will be continuing his long-standing development of laser processing using the FEL and ARC facilities. We congratulate Michael on his new position and welcome his closer collaborations with the FEL project.

Jock Fugitt is retiring Monday, 8 Feb 99. Jock has been the chief engineer for the FEL gun's high-voltage system and the FEL's high-power rf systems. We will miss him very much, not only for his vast wealth of experience, but also at a personal level. However, we are keeping him as a casual employee because Jock wants to contribute to the planned "20 kW" FEL upgrade. He'll be back!

FEL Installation/Maintenance Activities

A fast photodiode was set up in the Drive Laser Clean Room to support further study of the phase drift of the drive laser relative to the buncher cavity.

The molybdenum mirror sleeves were received. A sapphire ("3 µm") mirror will be mounted in one of the sleeves and tested next week.

Approximately 80% of the machine protection system was verified to be operational during the heat-clean cycle of the photocathode. The balance will be done next week.

FEL Commissioning Activities

The Laser Safety Operating Procedure was signed off for Lab 1 of the FEL Facility. It permits the first experiment to be set up and run in User Lab 1.

The plan for the week was to resume commissioning with electron beam. Unfortunately, once again the gun is acting up and we cannot generate useful electron beam. On Monday, following last Friday's cesiation, the gun was found to field-emit at 280 kV. Therefore we did another round of "cathode prep": high-voltage processing to 518 kV, followed by heat cleaning for 8 hours at 675 C, followed by cesiation. Thursday we again tried to bring up the voltage, but the gun field-emitted at 318 kV. Consequently, we decided on one more round of cathode prep. This time we will process to the highest achievable voltage, ~570 kV, do a long heat clean, and cesiate once more. High-voltage processing started last night and will continue until midnight today (5 Feb 99). It will probably not be complete by then, so most likely processing will continue Monday, with heat cleaning Monday night, and cesiation/turn-on Tuesday.

Plans are ready in case this last round fails. To summarize, if it does, we will try dry-nitrogen processing, with which SLAC has had some success. Failing that, we will open the gun and replace the cathode ball with a spare having a geometry modified for reduced peak voltage and, hopefully, concomitantly reduced field emission. We also will replace the cathode wafer since the present one has poor quantum efficiency. We will cesiate and test the photoresponse of the wafer prior to high-voltage processing to ascertain at what point the quantum efficiency degrades, i.e., prior to installation or after installation. The turn-around time for gun rework would be ~5-6 weeks. We hope to turn the gun on next week; the machine is otherwise ready to go.