The faulty 2F02 BPM was replaced this past weekend.

The 4F region and most of the 5F region was realigned this week.

Commissioning Activities

There was no beam operations this week. Last weekend, expecting to be checking out diagnostics (specifically the Happek devices) in some depth through the week, we heat treated the cathode so we could start fresh. On Monday afternoon, after cesiation, we attempted to ramp the gun voltage to 350 kV without using the conditioning resistor. Unfortunately the gun began arcing at 300 kV. We therefore inserted the conditioning resistor and did high-voltage processing overnight and part of Tuesday, eventually reaching 420 kV. After recesiation, the photoresponse of the cathode was very poor. Consequently we did another heat-treatment cycle and recesiation, but could not get past 318 kV without arcing. There was evidence of field emission from the cathode itself, and so we were concerned that arcing had splattered impurities over the gun's interior as had happened early February. Therefore we decided to polish the surfaces electrically, i.e., do more high-voltage processing. It turned out to be very easy to go back to 420 kV, where the gun sat quiet, and from that we concluded the cathode is bad but the gun's surfaces are not likely to be contaminated with splattered material. Consequently we decided once again (last night) to recesiate in hopes the cathode would recover. It did not, but exhibited field emission at 350 kV. Thus, today we opened the gun to proceed with changing out the wafer. We also developed a detailed timeline for refurbishment, and the entire process will take two weeks. If all goes well, beam operations will resume 1 Jun 98.

This week's developments were certainly unplanned and constitute a minor setback; however, the downtime will enable us to turn attention to other productive activities that had been languishing. For one, we will be able to complete a great deal of remaining short list of installation tasks, including in particular the second 180-degree dipole magnet. Two weeks from now the recirculation arc will be substantially complete. Still missing will be the sextupole magnets, due in late July, some air-core correctors, and the beam scrapers.

Happek (Univ. of Georgia), it turns out, could not visit this week after all because he was unable to complete fully his instrumentation. Thus the downtime enables him to finish carefully his two interferometric bunch-length monitors and to install and carefully check them out without beam. G. Krafft continues to work with Happek to coordinate completion of the diagnostic and arrange his visit. At this writing (1555, 15 May 98), he is planning to arrive here Monday, 18 May 98.

The time also gives us a much-needed opportunity to digest what we have learned thus far about the machine, and to write detailed procedures for establishing "lasing-quality" electron beam.