the laser was optimized with cw electron beam, and an output power of 311 W was achieved, as measured with a power head installed in the vault at the outcoupling mirror. In pulsed mode with a 1.2% duty cycle, the power measured upstairs in the Optical Control Room was 4.1 W, indicating a power during the macropulse of 340 W (we had no power head at the outcoupling mirror during this run). Assuming 15% losses in the optical transport line (a number that still needs to be measured), this corresponds to 400 W out of the laser. Lasing with an intracavity power of 3 kW therefore reduces the power output by around 25%. When the laser was operated at 200 W (where the spectrum is narrow) it could be turned on and off very repeatably. When operated at 300 W the cavity length had to be adjusted to reestablish lasing. CW lasing was quite stable and no degradation in performance was seen over a couple of hours of operation. In fact the laser seems to operate better as the cathode degrades, as long as the bunch charge can still be produced.

Yesterday's day shift was spent toward improving the match of the recirculated electron beam. Yesterday evening we were preparing to do another run of cw lasing straight ahead to try out some ideas for improving the cw laser power and also to measure the loss in the optical transport line. Unfortunately, the gun arced twice, and later a third time, polluting the cathode and severely degrading its quantum efficiency. We still did some lasing at 10 pC bunch charge, but could not carry out our plans for the evening. This morning, the maximum bunch charge that could be extracted was only 5 pC. The gun had to be operated all week at voltages in the range 324-330 kV because field emission was problematic at the nominal 350 kV. It also needed daily recesiation. Nonetheless, we achieved the successes described above.

Detailed plans for the next two weeks were developed. We will use the weekend to try to bring the gun back online. Next, we will work further to improve the match of the recirculated beam, then set up both the beam-loss monitors in the recirculation loop and the energy-recovery dump to permit cw recirculation, then do cw recirculation with energy recovery, and then lase cw with energy recovery with an average electron current of at least 2.2 mA. If all goes well, and if we can get the necessary Laser Safety System and Laser Safety Operating Procedure fully completed, we may also be able to squeeze in a user experiment in Lab 1 (that being prepared by M. Shinn and Old Dominion University). We will accomplish all we sensibly can prior to the FEL Conference, which will start here in Williamsburg on 16 Aug 98 and end on 22 Aug 98. The FEL will be open (no running) during the Conference.