Free-Electron Laser Commissioning Meeting

Monday, 1 Mar 99
Recorder: C. Bohn

Next Meeting

Date: 5 Mar 99 (this Friday)
Time: "0845"-0915
Place: FEL Facility Break Room

Agenda for Next Meeting

Brief discussion of this week's progress and what we'll do during the following 1-2 weeks (e.g., user "tests" vs. injector work and/or other machine development vs. more power vs. ...).

This Week's Attendees

S. Benson, C. Bohn, J. Boyce, D. Douglas, F. Dylla, R. Evans, J. Gubeli, K. Jordan, R. Li, L. Merminga, G. Neil, P. Piot, M. Shinn, T. Siggins, R. Walker, B. Yunn

Closed Action Items

New Action Items

Old Action Items

None.

Items of Discussion

C. Bohn opened with a review of shift assignments. As always, the FEL commissioning team should stay abreast of the 2-week schedule on the FEL white board and/or the Web posting thereof.

The attendees had a freely flowing discussion concerning the status of the machine and the game plan for the next two weeks. Many details surfaced, but the bottom line is this:

  1. Most likely the FEL is still cathode-limited in the sense that given a "60 pC" cathode QE, we are unsure whether we can recirculate the corresponding average current without tripping. We had been limited by IR detector interconnect trips in the srf waveguides, and we began masking the detectors (with suitable administrative control!) only late last week at a point that the cathode QE had degraded. Thus, we will recesiate the gun today (Monday), and tomorrow morning inject the highest possible current with the detectors masked. We will then see if we can establish transport settings to recirculate the current with strong lasing, e.g., try to establish another power record (for reasons of external politics and marketing).
  2. We will try to ascertain whether we have reached a thermal limitation in the optical-cavity mirrors by doing a power vs. optical-cavity length scan in both cw and pulsed modes at 37.4 MHz and at high current and laser power. If the answer is unambiguously "yes", then we will make plans to install the silicon reflecting mirror (which should about double the thermal limit).
  3. We will send laser beam into User Lab 1 all this week on Swing Shift (and on Day Shift if we reach an impasse on high-power runs).
  4. We will continue diagnostics work on Owl Shifts related to the CSR experimental program.
This Friday we will meet again and plan the following week based on the outcome. If the machine proves to be transport-limited, and if we have done the readily available user "tests", then we will likely begin the much-discussed injector setup program. Otherwise, we'll continue the "traditional" program as long as the gun holds out, or maybe we'll just party!

One possibly important detail was raised by S. Benson, namely in view of a persistent pressure rise prior to the cryounit that seems to be commensurate with average current, he suspects a possible rf instability induced by the buncher cavity. That cavity is known to be problematic in the sense that its thermal-control loop is designed for 2 kW input, not the few hundred watts we use. C. Hovater and C. Pillar are aware of the control problem and are exploring ways to circumvent it. Meantime, we should stay conscious of Benson's suggestion.

The urgency of the need to rework the crinkled ITV1G01 viewer was discussed at some length. It impedes setting up the longitudinal phase space of the recirculated beam, and therefore may be making it more difficult to mitigate scraping in the energy-recovery dump line. Depending on how things progress this week, we may need to insist on its replacement next Monday.

Benson closed the meeting with an overview of his procedure for cataloguing the "Golden Orbit" to restore machine unambiguously. The procedure is systematic and based on the methodology and software used in CEBAF. Bohn asked him to prepare his thoughts in the form of a document to be posted as a procedure both on the Web and in the relevant Control Room binders.

New Issues

None other than those mentioned above.