Next Meeting
Agenda for Next Meeting
Item Person Responsible Time ---- ------------------ -------- Status of Open Action Items All 5 min Scheduling and Commissioning Program Bohn/All 50 min New Issues All 5 min
This Week's Attendees
J. Bennett, G. Biallas, J. Bisognano, C. Bohn, J. Boyce, R. Evans, J. Fugitt, A. Hofler, C. Hovater, K. Jordan, R. Lauze, R. Li, L. Merminga, D. Oepts, J. Preble, M. Shinn, Q.-S. Shu, T. Siggins, R. Walker, B. Yunn
Closed Action Items
Items of Discussion
This week was devoted principally to fine-tuning the electron beam as part of preparing for lasing, and to miscellaneous measurements of beam quality, with cw runs interspersed to exercise the machine and gather more data on cathode lifetime. At week's end, we had a machine setup for which the electron beam is centered through all of the beam-transport magnets. There is considerable horizontal-vertical coupling out of the cryomodule, and so we need to install skew quadrupoles at both ends of the cryomodule to cancel out the coupling. A consequence of the coupling is that the beam rotates through the wiggler region so that there is scraping on the narrow wiggler vacuum chamber of a magnitude that prohibits cw runs with this setup. Once the skew quads are in, this should no longer be a problem. They are already in fabrication and are slated to be installed Tuesday, 5 May, which is the next maintenance day. On the positive side, results of difference-orbit measurements taken this week are entirely consistent with model predictions. Thus far the machine settings generally remain stable as long as its hardware is not modified. To do the cw runs, we used the machine settings from late last week. They permit high average current but are not well suited to be used as baseline settings for lasing.
Multislit #2, located at the input to the cryomodule, was found to be rotationally misaligned. Its alignment was corrected, and one can now see a small number of slits in both the horizontal and vertical directions. An earnest attempt to take data with Multislit #2 has not yet been made due to a bug in the user-interface code that is in process of being corrected. The beam at Multislit #1, located at the exit of the cryounit, tends to be too small to submit to accurate measurements of emittance. Indications now are that the machine setup we are fine-tuning provides emittances at Multislit #1 in the range 4-6 mm-mrad, versus the PARMELA prediction of 3.5 mm-mrad. We need to devise a procedure that involves an off-nominal setting of the quadrupole magnet immediately preceding the diagnostic.
The zero-phasing technique to measure bunch length was further refined this week, and at week's end was limited by scraping at the low-energy edge of the bunch during transport of the beam through the machine to the energy-recovery dump, a circumstance that needs to be rectified. The quad/viewer measurement of emittance at the wiggler location was also further refined but still needs more work. Presently, multimonitor data suggest, at the wiggler, an emittance of 7.0±3.5 mm-mrad in the horizontal direction, with the vertical direction still uncertain. We are trying for <8.7 mm-mrad for first light.
As a general procedural matter, R. Lauze reminded everyone of the wisdom in recycling the magnets through their hysteresis loops after restoring machine settings. Failure to do this can confound the beam dynamics and, concomitantly, measurements of beam quality! CEBAF operators are keenly aware of this, so again we are advised to make sure they are used as an integral participant in each shift.
Happek and crew from the University of Georgia are now scheduled to be here next week, from 4-9 May, to install and commission their interferometric bunch-length monitors. (Late-breaking development, at 1430: Happek now says he'll be here from 7-13 May 98.)
Next week the basic program is to do orbit optimization during day shifts and beam diagnostics/beam quality measurements during swing and owl shifts. The following week is devoted to continued beam optimization during day shifts, with cw running during swing shifts and beam-quality measurements during owl shifts. The goal is to be able to insert the wiggler in mid-to-late May and try to lase. It is an optimistic goal, but one that seems to be within reach.
Shift assignments for the next two weeks are (remember to use the CEBAF operator!):
Developments in the last two weeks point to an unambiguous need for increased emphasis and discipline on matters related to configuration control of the machine. As a result, R. Walker and C. Bohn drafted a simple form that will need to be filled out, appropriately coordinated, and approved through the FEL Commissioning Coordinator prior to carrying out any change in the machine configuration, be it hardware or software. The form was refined at this meeting, and will be finalized today. Plans are to put it in a Framemaker template and have it accessible from our control system by way of the third mouse button. (Note added at 1400: Walker ascertained that it is far easier, quicker, and more convenient to add a link on the www FLOG page, so that is what he will do.) Walker will complete this action and monitor the status of the work, partially by way of the daily 0830 meetings in the FEL Facility. One comment: the form covers configuration change, and it is not needed for repairs that do not constitute configuration change. This whole matter is a temporary measure, but it will not be lifted before the machine configuration settles down to its steady state.
Status of the remaining top-level MUST-priority prerequisites to lasing is:
1.Stable, easily recoverable 1.1 mA, 38 MeV beam with sufficiently good
beam quality.
New Issues
There was some discussion about the need for routine system checks, specifically checks of arc detectors and BLMs. Walker and Bohn will investigate off-line.
New Action Items
Old Action Items
Test Plans in Work
Procedures in Work
Set Up Longitudinal Phase Space Douglas, 15 May 98 Set Up Transverse Phase Space Douglas, 15 May 98 Set Up Beam Steering Douglas, 15 May 98 Emittance Growth from CSR
Procedures Needed for Recirculation