Management

Highlights for the week: the IR Demo is back on the air; one day into operations we pushed with recirculation current with lasing to a new record–2 mA.

The paperwork for operational readiness of User Lab 1 is under final review by the Laboratory Safety staff. Several modest user demonstration experiments with the FEL will occur in this laboratory. They include a polymer amorphization experiment by CWM/DuPont, a pump-probe IR spectroscopic experiment by JLab staff, and a laser-material interaction study by the Naval Postgraduate School.

FEL Installation/Maintenance Activities

The predominant activity was bringing the photocathode gun on-line, albeit at the off-nominal voltage of 330 kV. The cathode quantum efficiency presently supports 60 pC operation.

FEL Commissioning Activities

After another round of high-voltage processing, heat cleaning, and cesiation, we decided to "punt" with respect to requiring the gun to operate at the full 350 kV level. Specifically, we found the gun will hold voltage at 340 kV and the cathode will support 60 pC bunch charge. So, we elected to set the voltage at a conservative 330 kV and run (!) starting Wednesday evening. As of this writing (12 Feb 99, 1700), we had already accomplished a number of things, including commissioning all of the new diagnostics, successfully running at 75 MHz repetition rate, and recirculating slightly more than 2 mA cw at that rep rate while lasing at 50+ W. We were limited by waveguide IR detector trips (as during last December's run), which we will have to spend more effort toward understanding. We also were limited by some beam scraping around the cryomodule exit, meaning the transverse properties of the recirculated beam need further improvement. Tonight's shift is dedicated to lasing studies in support of further commissioning of the FEL systems and diagnostics.

Plans for this run are to try to achieve another cw power record (maybe ~500 W?), possibly send some light into one of the user labs, and then turn off (in ~3 weeks?) for a gun rebuild. Based on recent history, we suspect the cathode ball has been splattered with metallic contaminants since the last few cathodes have been, and so we plan to replace the ball with an existing spare. We also plan to install a "focused" cesiator to cut down on cesium deposition on the electrodes. And we are modifying certain hardware used in deuterium-cleaning of our cathodes, after which we suspect the quantum efficiency will be better. The present run with the "off-normal" gun buys us time to prepare for the gun rework, while also permitting us to make further progress on commissioning.