I held an impromptu meeting of members of the FEL Commissioning Team who were present in the FEL Facility this morning. My goal was to apprise people of where we were and make sure everyone was in resonance as regards to where we're going. Matters of discussion were as follows:

0.    1 kW vs. Configuring a User Lab: Apparently conflicting mandates have been passed down to the Team. I and some others regarded our clear priority to be establishment of kW-level performance, a commissioning-intensive task. Our I&C team regarded the priority to be setting up a User Lab and getting its LSS ready. These tasks are not mutually exclusive; they overlap. Diagnostics experts (including members of the I&C group) have been "traditionally" assigned to Owl Shifts for intensive beam diagnostics that feed into machine setup during Day and Swing Shifts. The group is feeling stressed, and with their perceived priority combined with my direction, they feel it impossible to satisfy their requirements. Bohn will discuss the matter with F. Dylla.

I.    Gun Cathode: Today the cathode is putting out 45 pC at most. At 37.4 MHz, we can in principle achieve about 1.6 mA recirculated beam, whereas to date we have achieved "only" 1 mA cw recirculated beam (at 37.4 MHz while producing >100 W cw laser power as measured upstairs, meaning about 140 W out of the FEL proper), after which either BLM or rf trips have been showing up. Consequently 45 pC suffices to enable continuing the machine setup. L. Merminga is on Day Shift this week; she will be checking whether rf transients are influencing the machine setup. But, the cathode is deteriorating. Plans are as follows:

• Recesiate Friday Day Shift, 11 Dec 98, unless it is needed earlier. If the gun comes up well, resume running Friday Swing Shift. If not, heat clean over the weekend, do high-voltage processing and another short heat clean, then remake the cathode -- resume running sometime the following Tuesday or Wednesday.

• Replace the wafer immediately after Christmas break -- it is due to be replaced. Downtime will then be 23 Dec 98 through 19 Jan 99, exactly in phase with the planned downtime of CEBAF, meaning we will not have conflicts with lack of MCC staffing.

II.    Achieving 1 kW: Presently, as mentioned above, we've achieved a little over 100 W cw laser power measured upstairs in the FEL Optical Control Room (~140 W downstairs) with about 1 mA cw recirculated beam. We need another order of magnitude, and we're working on it. The plan by which we will be proceeding is as follows:

• Achieve 60 pC, 2.2 mA cw recirculated beam in the presence of moderate lasing; gradually increase the strength of lasing.

• Raise the bunch charge to 80-90 pC; achieve ~3 mA cw recirculated beam, ultimately with strong lasing.

• Increase the repetition rate to 75 MHz with 60 pC bunch charge to achieve ~4 mA cw recirculated beam, ultimately with strong lasing. (Note: This is nontrivial in that the associated beam mode is not presently configured into the MPS; it had not been part of our initial planning, and K. Jordan estimates it could not be available prior to mid-Feb 99.)

• If/when lasing is limited by the present photon optics (we don't yet know conclusively where the limit is!), then:
  • replace the existing downstream mirror with an available, more highly reflecting silicon mirror; should roughly double the power ceiling.

  • replace the 5 micron optics with the sapphire (3 micron) mirrors; set up the machine for 48 MeV energy and 3-micron lasing. (Note: The sapphire mirrors are presently at the vendor after failing tests at China Lake. After modification is complete, they will be returned to China Lake for further tests. If they pass, we'll get them from China Lake. Bottom line -- they probably won't be available for a couple of months.)