In mid-May we lost our photocathode due to an arc in the gun and had to replace it, a two-week task. Consequently we did not run during the last half of May, but we used the down time to complete most of the remaining installation and to work on additional procedures needed for setting up the machine to provide the beam quality necessary for lasing. Commissioning with electron beam resumed 1 Jun 98.

As a general remark, phase-space parameters that have been measured thus far generally fall within a factor 2-3 (far less than an order of magnitude!) from those required for lasing. Of course, if all parameters were double the requirement, no lasing could happen. The point is that the data continue to suggest we're within reach but need to continue fine-tuning the beam before installing the wiggler. That will be our focus as we resume commissioning in June.

Development of additional procedures proceeded systematically starting with augmentation of a "Phase Space Setup Metaprocedure" that was prepared based on commissioning progress to date. For example, another systematic procedure for setting up the RF gradients and phases in the cryounit was written. We now have three methods for cryounit setup, and after turn-on we are planning to implement all three in an effort to reconcile them and get them to agree. Other procedures drafted this month concern resteering after rephasing the cryounit, phasing and gradient calibration of the cryomodule cavities, and rematching to the wiggler and dump. We also updated the procedure for difference-orbit measurements, and we completed a set of numerical simulations to ascertain better the expected beam quality at the locations of key diagnostics.

We did some hardware checks of the drive-laser RF system to ascertain phase drifts and amplitude noise. Nothing dominant has been found to date, but the process is continuing. We also put together a plan to model the drive-laser RF system and expect to complete the modeling in about a month.

Dr. Uwe Happek of the University of Georgia visited us near the end of the month. He delivered the hardware for the two interferometric bunch-length monitors and assisted with their fit-up. Preliminary indications from off-line tests are that the Happek devices, particularly their radiation detectors (Golay cells), perform very well.

FEL INSTALLATION

Installation highlights in May included:

The near completion of the FEL systems. The calcium fluoride first-light mirrors were installed. Alignment of the cavity mirrors as viewed through position sensors drifted by less than 10 µrad over several days, well within specification. By month's end, the FEL systems in the vault (notwithstanding that the wiggler is not installed there) were ready for lasing. Diagnostics in the Optical Control Room were nearly finished, and the supporting Laser Safety System will be