Next Meeting

Date: 14 Nov 97

Time: 0830-0930

Place: FEL Facility Break Room

Agenda for Next Meeting

                Item                             Person Responsible     Time
                ----                             ------------------  --------
Review of Minutes/Errata                                All             5 min
Scheduling Update                                       Bohn           15 min
Progress Report on Injector Commissioning               Legg            5 min
DQ Dipoles (and other relevant magnet stuff)            Douglas        10 min
Master Oscillator System Status and Data                Musson         15 min
New Issues                                              All             5 min
Agenda for next week                                    All             5 min

This Week's Attendees

J. Bennett, J. Bisognano, C. Bohn, J. Boyce, D. Douglas, D. Engwall, A. Grippo, R. Legg, R. Li, L. Merminga, G. Neil, P. Piot, J. Preble, Q.-S. Shu, R. Walker, M. Wiseman, B. Yunn

Addenda/Errata to Previous Minutes

The following actions from last week's report were closed out:

• FEL Commissioning Team: Enjoy ARM training. Status: Seven FEL Commissioning Team members attended ARM training last week: S. Benson, C. Bohn, R. Hill, G. Neil, M. Shinn, T. Siggins, and R. Walker. G. Neil scored the highest grade on the test, so he'll be first up! As for untrained FEL ARMs, your time is coming.
• Legg: Develop rough estimate of the frequency for recharging the photocathode in light of recent vacuum measurements. Status: The e-folding time for cathode "death" by oxygen impingement is, per very rough estimate, eight weeks. This means we can anticipate rebaking the gun in January, which is an acceptable scenario.
• Walker: Ensure rf processing of the buncher cavity is scheduled at the daily 1145 scheduling meeting. Status: The buncher cavity was vacuum-processed at 3 kW. It will be run by MCC operators over this weekend for an assessment of its stability.
• Walker: E-mail two-month shift schedule on 31 Oct 97. E-mail updates as they arise. (done 31 Oct 97, appropriate follow-up needed) Status: E-mail accomplished.
• Walker/Legg/Bohn: Assign tasks to the November shifts. Post shifts/tasks on the FEL Facility Break Room white boards. E-mail the information to affected (infected?) individuals. Status: Tasks for the next two weeks are posted in the FEL Facility Break Room, as best as they can be projected at this time. The boards will be updated as appropriate. FEL activists should peruse it routinely.
• Bohn: Find out date of availability of model server. Status: Bohn and C. Murray provided S. Witherspoon with nomenclature drawings for the magnet and diagnostic systems. She is incorporating the nomenclature in the model server, which was ready excepting this activity. First cut should be available early next week, and final version is projected in a two-week time frame.
• Douglas: Assess utility of spare CEBAF air-core correctors with tune-up beam to the straight-ahead dump. Status: They should suffice provided they fit. The biggest concern is in the optical chicanes.
• Piot: Estimate resource requirements for developing software for automating acquisition of phase-space-tomographic maps. (due 27 Oct 97) [Note: Task complete, except Bohn needs to follow up with J. Song to ascertain his work load. Will do by 4 Nov 97.] Status: Song is completely occupied with higher-priority FEL software tasks for the next two weeks. In the meantime, Piot should try to run the software he got from www (listed below as a new action). This will give an indication as to the required work load.

In addition, L. Merminga announced that she has finalized the procedure "Cryomodule Setup -- Set Cavities to Nominal Gradient".

Items of Discussion

The MCC-like scheduling boards are now mounted in the FEL Facility Break Room. Immediately following this morning's meeting they were filled out with the shift tasks projected for the next two weeks.

R. Legg and J. Preble presented this week's injector commissioning highlights:

• The leaky vacuum seal for the rf warm window in the cryounit was replaced, and the cryounit was successfully cooled down on Tuesday, 4 Nov 97. SRF commissioning subsequently commenced. At this writing, the exit cavity has been operated at cw gradient in the range 8.0-8.7 MV/m, and at 10.5 MV/m pulsed. CW performance is limited by the IR interlock, and some consideration is being given to whether the IR fault limit should be set less conservatively. Plans are imminently to operate the entrance cavity and determine its maximum useful gradient. There is a possibility that the cavities can be run at, e.g., 12 MV/m and 8 MV/m, respectively, rather than the 11 MV/m and 9 MV/m gradients that had been projected based on results from earlier off-line tests in the Injector Test Stand. Yunn will begin PARMELA modeling to support srf commissioning and help determine whether resetting the IR interlock limit is necessary.
• Vacuum processing of the buncher cavity took place, during which it was operated to 3 kW.
• A training video was made showing operator screens used to transport beam from the gun to the first viewer.
• Connections to the injection-line dipole magnets were completed, and these magnets were powered to 50 A.

J. Boyce discussed plans to use tune-up beam from the FEL to produce polarized targets in support of Nuclear Physics' GEN experiment. The plan is documented in Jefferson Lab Tech Note #97-041 entitled "A User Station for the FEL Beam Dump". It involves installing a dewar in the first-light dump line, with the dewar containing a solid ammonia target cooled by liquid argon or liquid nitrogen. After irradiating the frozen ammonia crystals with low-current electron beam to produce paramagnetic centers, the crystals can then be immersed in a strong magnetic field and exposed to microwave radiation, both in situ in the CEBAF experimental hall, to achieve the desired polarization. Optimal timing for use of the FEL for target production is early February. Accordingly, installation of the apparatus in the dump line is anticipated for January 1998. Our commissioning plan is to have tune-up beam at the first-light dump before Christmas 1997.

Boyce pointed out that 10 MeV electrons would suffice. G. Neil suggested that, while commissioning the injector, we may find that sufficient electron current penetrates through the copper block constituting the injector dump. If so, the dewar could then simply be positioned after the copper block. Consensus was to keep that option open as a potential back-up, but to continue planning as a baseline for installing the dewar in the first-light dump line. Doing so helps to motivate steady progress in commissioning, and is in keeping with existing hardware designs.

G. Neil advised that the vacuum pump designed into the first-light dump line is insufficient, and indicated that a 120 l/s pump is needed. M. Wiseman said the Mechanical Engineering Group is aware of the concern and is looking into it. (This appears as a new action item below.)

D. Douglas went through his draft procedure for "Beam Transport Setup from Cryomodule to First-Light Dump". It appeared to be complete, except for overlooking the need to do longitudinal phase-space diagnostics. The two interferometric bunch-length monitors, including both hardware and software, are due here from the University of Georgia on or about 5 Dec 97. In turn, they probably will be unavailable for use in commissioning with tune-up beam prior to Christmas, but they likewise are unnecessary for that task. As we turn up the average current in early 1998 to produce electron beam for first light, the bunch-length monitors will then be essential, and they should be commissioned beforehand per the Diagnostic Integration Plan. Douglas will augment his procedure to include longitudinal measurements.

New Issues

• Field measurements of the reverse-bend (DQ) dipoles indicate that they provide a working aperture that is too small, roughly a four-inch good-field region as opposed to the desired eight inches. D. Douglas reported that DIMAD analysis shows consequent orbit variations in the off-momentum beam at the several-percent level. The FEL "Magnet Team" is working to develop a viable plan in view of the results. Douglas will give an update at next week's meeting.

• TOSCA modeling of the injection/extraction (DV) dipoles is ongoing to resolve how to counter unwanted fringe fields across the Y-chambers, but progress has been slower than anticipated. One of these magnets must be installed within two weeks to support getting tune-up beam to the first-light dump before Christmas. This could conceivably be facilitated by, for example, symmetrizing its field clamp and using a corrector to counter remanent fringe fields. D. Douglas will work with J. Karn to devise a strategy.

New Action Items

• FEL Commissioning Team: Inform C. Bohn and R. Legg by e-mail if you are planning vacation during Thanksgiving week. (due 10 Nov 97)
• Piot: Do preliminary tests of tomography software obtained from www. (due 14 Nov 97)
• Yunn: Model cryounit with cavity performance set at 12 MV/m and 8 MV/m for the entrance and exit cavities, respectively. Feed information to J. Preble, and iterate as required. (due in real time to support ongoing srf commissioning of cryounit)
• Douglas: Develop with J. Karn, et. al. an installation strategy for the DV dipoles consistent with FEL commissioning milestones. (due 10 Nov 97)
• Douglas: Lead the "FEL Magnet Team" toward developing a viable plan for resolving the DQ good-field problem. (due 14 Nov 97)
• Wiseman: Determine vacuum-pump requirements for the first-light dump line. (due 12 Nov 97)

Old Action Items

• Legg: Resolve issue of inductive heating of straight-ahead dump line. (due 7 Nov 97) Status: Based on CEBAF experience, this appears not to be a problem provided the pipe thickness is less than 1 mm, but the calculation still needs to be done. Legg will do it this week.
• Biallas: Check on availability of spare CEBAF air-core correctors. (due 10 Nov 97) Status: Air-core correctors for the straight-ahead beam line are scheduled to be received from the vendor just after Thanksgiving. If all goes well, we may need air cores about one week before Thanksgiving in keeping with the Commissioning Plan. Biallas will look for CEBAF extras.
• Bohn: Work with M7 to identify system owners and their responsibilities, maintenance provisions, and escalation policy. (due 7 Nov 97) [Note: M7 tasked Bohn to draft a detailed list of maintenance group leaders for the various FEL systems. Once complete, Bohn will brief the FEL Commissioning Team.]
• Bohn: Work with M7 to establish criteria for transferring the FEL as a user facility to the Operations Department. (due 30 Jan 98) Status: Transfer will likely occur when the machine works. This task is to define the meaning of the infinitive "to work".

Procedures in Work

First Light Setup

Thread to Straight-Ahead Dump               Douglas, finalize by 1 Dec 97
Dump Setup                                  Legg, finalize by 1 Dec 97
CW Setup                                    Legg, 1 Dec 97

Emittance Growth from CSR

Tomographic Phase-Space Map                 Piot, 1 Dec 97?
Back Leg Thread                             Douglas, 1 Dec 97

Thread Beam around Machine, Top-Level           Douglas, 1 Dec 97