To: J. Cook, D. Helms, W. Skinner

cc: Division (M7), FEL Coordination Group

From: F. Dylla

Subject: IR Demo Project Weekly Report, September 21-25, 1998

Date: September 25, 1998

Management

This week we attempted to re-start operations after the month long shut down. The highlights of the week include (1) collection of useful data on the photogun high voltage conditioning process; (2) detailed check-out of the full Machine Protection System (MPS).

On Tuesday, Sept. 22, the project monthly report for August 1998 was submitted to the DOE and Navy program offices.

On Wednesday, Sept. 23, F. Dylla, J. Boyce and R. Lusk attended DOE's program review for the ER Laboratory Technology Research (LTR) Program. The FEL Project is submitting a proposal to the LTR office for support of the FEL User Labs in FY99-01.

FEL Installation/Maintenance Activities

The following tasks were completed this week ("*" denotes higher-priority tasks):

*Installed lead bricks for camera shielding.

Installed multiplexer for the Analog-Monitoring System (AMS); 64 of the 128

AMS channels are now configured.

*Checked Drive Laser alignment for loss of SHG power.

*Added a temporary corrector magnet at the end of the injection line.

*Installed differential-pump transducer for the beam-scraper

low-contamination water system.

Added camera to view the energy-recovery dump face.

*Installed geiger tubes to monitor x-rays during high-voltage processing of

the gun.

FEL Commissioning Activities

Dr. Peter Michel arrived from Rossendorf Laboratory, Dresden, Germany, on a three-month sabbatical to work with us. Michel is responsible for the electron-beam diagnostics for Rossendorf's superconducting FEL that is now under construction, so he will focus on diagnostics and gain experience with machine operations during his stay.

High-voltage processing of the gun at 420 kV was completed over the weekend. The cathode was heat-treated Monday and, after cooldown, was cesiated Tuesday afternoon. Unfortunately, and surprisingly, two problems subsequently arose. First, the photoresponse of the cathode after cesiation was very poor. Second, field emission down the beamline showed up at around 300 kV. A plan to diagnose the problems was formulated Wednesday and implemented yesterday. The outcome is that, with high probability, the source of field emission is on the front of the cathode ball but not located on the cathode wafer itself. This finding was ultimately established by retracting the cathode and discovering the same field-emission spot at the same location and roughly the same voltage. PARMELA calculations affirmed the front of the ball is visible on the ceramic viewer at the solenoid settings that were in place during the observations. During the process of diagnosis, the cathode was observed to have "nonexistent" quantum efficiency (QE); observable electron beam could not be extracted from the cathode even when it was subjected to full pulsed-power drive-laser light. There was a small vacuum leak during a portion of the bake, and one conjecture is that the wafer oxidized as a result of the leak. If so, it will need to be replaced, but presently there is insufficient data to establish a conclusion concerning the bad QE.

Immediate plans for gun work were formulated this morning. The resultant plan is as follows:

- High-voltage process to 420 kV (or as high as sensible) today, with the cathode retracted, to burn off the field-emitter.

- Heat-treat the cathode (675 C for ~2 hrs) late today, let it cool over the weekend.

- Insert the cathode Monday morning and cesiate it.

- Run the gun Monday afternoon.

- Make another GaAs wafer and mount it on the spare stalk today as a backup.

- Machine a cathode mask today.

If the gun does not work Monday afternoon, then:

- Process the gun with He gas at 400 V Tuesday to drive off impurities.

- Heat-treat the cathode (675 C for ~2 hrs) Wednesday morning; let it cool for ~16 hrs.

- Cesiate the cathode Thursday morning.

- Run the gun Thursday afternoon.

- If the gun still does not work, begin cathode-replacement activities Friday.

At this writing (1600 Friday, 25 Sep 98), the planned work is in progress and the gun was successfully processed to 420 kV. Auger analysis of the last cathode will commence next week, and people are being prepositioned for Auger analysis of the present cathode once it is extracted.

A detailed checkout of the MPS ensued this week. The essential findings thus far are: all MPS hardware is now operational; however, user-friendly screens are generally lacking, with many indicating "invalid beam mode" without pointing to the specific cause. The Safety Systems Group is apprised and will need to improve the screens by labeling the various channels. Signed-off certification of the MPS should occur today. MPS documentation still needs to be completed; work to that end is in progress. One detail concerns the dump-line quadrupole magnets; current limits from these magnets will not be inputs to the MPS because there is already a redundancy of protection for the dumps (vacuum, water temperature, and water flow), and the quads will need to be adjusted as beam parameters, e.g., energy, are changed to Accelerator Division management for formal approval as a FY99 task.