Free Electron Laser Commissioning Meeting

Friday, 24 Apr 98
Recorder: C. Bohn

***** SEE PERSONNEL SAFETY AND MACHINE PROTECTION POLICIES UNDER NEW ISSUES BELOW *****

Next Meeting

Date: 1 May 98
Time: "0845"-0945
Place: FEL Facility Break Room 


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

S. Benson, G. Biallas, C. Bohn, J. Boyce, D. Douglas, F. Dylla, J. Fugitt, A. Grippo, L. Harwood, K. Jordan, R. Li, L. Merminga, D. Oepts, P. Piot, M. Shinn, Q.-S. Shu, R. Walker

Closed Action Items

Items of Discussion

This week was devoted principally to miscellaneous measurements of beam quality, as well as improving the injector setup, but it also included a few cw runs up to mA-level average current at 38 MeV energy to the straight-ahead dump. We are generally measuring six-dimensional phase-space parameters of the beam that are within factors of 2-3 of theoretical, a favorable situation given that we just turned on the machine. It means there are no apparent show-stoppers to lasing, but fine tuning is needed beforehand. Specific measurements performed this week include rms normalized transverse emittance at the cryounit exit (7-8 mm-mrad vs. 3.5 mm-mrad from PARMELA), rms bunch length at the center of the cryomodule (about 2 ps, vs. 1 ps desired at the wiggler), rms energy spread at the center of the first optical chicane (0.5% vs. 0.15% desired at the wiggler), and a rough sense that the emittance at the wiggler is not too far from the 9 mm-mrad desired in that most of the electron beam can be threaded through the mm- size holes in the three wiggler viewers. Getting a sufficient array of beam diagnostics working and using them to configure the quality of the electron beam at the wiggler location are now our highest-priority tasks. They will occupy the bulk of our commissioning time in the next two weeks, in which will be interspersed some cw runs at high average current to exercise the machine and get more data on cathode lifetime.

Shift assignments for the next two weeks are (remember to use the CEBAF operator!):

27 April - 1 May 1998:
Owl -- Oepts, CEBAF operator, Shu on standby
Day -- Li, CEBAF operator, Douglas on standby
Swing -- Benson, CEBAF operator, Krafft on standby
4-8 May 1998:
Owl -- Preble, CEBAF operator, Piot on standby
Day -- Biallas, CEBAF operator, Douglas on standby
Swing -- Krafft, CEBAF operator, Shinn on standby
S. Benson presented a synopsis of electron-beam requirements for first lasing. They are documented in the talks for the "IR Demo Commissioning Workshop" held here during 24-25 Jul 96, so rather than repeat all the numbers, I'll give some of the principal ones: normalized rms transverse emittance <8.7 mm-mr, rms longitudinal emittance <33 keV-deg, beta function at wiggler 33+/-6 cm, energy spread <0.15%, peak current >22 A, rms bunch length <1 ps. It may still be possible to have sufficient gain for lasing even if some of these are not met, so long as others are better. Benson has developed a spread sheet to calculate gain given the beam parameters, and it will be our tool by which we determine when to install the wiggler and go for it. We will not install the wiggler until we have sufficient electron-beam quality and sufficiently stable and reproducible machine operation. We will not install the wiggler on "1 May 98", but we will be sensibly expeditious.

C. Bohn summarized a list of test plans and procedures to prepare for lasing that came out of an off-line meeting Wednesday. The list is incorporated at the end of these minutes, along with principals and due dates. The principals will be seeking help and advice as they write their respective documents.

There was some discussion about policies concerning personnel safety and machine protection. Bohn worked through the various questions in consultation with A. Hutton this morning, and the ensuing policies are documented under New Issues below.

Continuing from the last two weeks' discussions, a list of remaining MUST-priority prerequisites to lasing, and their status, is:

1. Stable, easily recoverable 1.1 mA, 38 MeV beam with sufficiently good beam quality.

Status: See Items of Discussion above.
2. Working diagnostics:
Status: Still not sure when Happek will be delivered. We are implementing a backup plan that will be useful in any case: G. Krafft is in process of procuring a CSR monitor for use at one of the synchrotron light ports in the first optical chicane. It can be used to "minimize" and monitor bunch length, and it can be calibrated against the zero-phasing technique. Energy spread can be measured at the first optical chicane with a viewer there and MaxVideo. The M_56 cavity provides additional longitudinal phase-space information.
Status: There is some question as to whether the Multislit #2 viewers are sufficiently well aligned. The beam needs to be orthogonal to the multislit to within 5 mrad for the device to work. Despite spanning through the entire accessible parameter space, attempts to correct the orbit at the viewers were not successful, which leads to the question. Work is still needed here.
Status: Tonight's swing shift is devoted largely to this item.

3. Adequate injector setup.
Status: Continuing. Not obvious we have a real problem here.
4. Detailed procedures and test plans well communicated to MCC staff.
Status: Ongoing. See, for example, list at end of these minutes.
5. Working optical transport, including Laser Safety System for the Optical Control Room.
Status: Largely, but not fully, complete.
6. Radiation monitor at wiggler location (to protect wiggler).
Status: Detector ready and will be tested shortly.

New Issues

Two irregularities in FEL operations occurred in the 24 hours preceding this meeting. First, during day shift yesterday the FEL console was left unattended with the drive laser shutter open. Second, during owl shift today one of the BLMs was intentionally masked and the beam was taken to cw without seeking approval from the FEL Commissioning Coordinator (FEL CC). These facts generated some broad discussion about general safety matters, and clarification is needed. After the meeting, Bohn met with A. Hutton and the outcome of the meeting is the following two policies:

  1. The MCC crew chief is in charge of personnel safety. The FEL PSS will continue to be operated from the MCC. CEBAF operators will man the Safety Console and will provide SSO functions.
  2. The FEL crew chief will exercise prudent judgment in matters of machine protection and is permitted to operate the FEL within the constraints of the FEL Operator Limits Page (FEL OLP) posted in the FEL binder in the MCC. FEL CC will maintain the FEL OLP. If the FEL crew chief sees benefit in operating outside one or more of these limits, that person must first contact the FEL CC for authorization and then document the fact that authorization was obtained. (Note: The FEL crew chief is the individual assigned as prime to the shift, and is neither the individual assigned as "standby" nor the assisting CEBAF operator.)

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
Checklist for CW to Pulsed and Vice Versa       Walker, 24 Apr 98
Emittance Growth from CSR





Procedures Needed for Recirculation



Thread Beam around Machine, Top-Level           Douglas, finalize 30 June 98
RF Stability during Energy Recovery             Merminga, 30 June 98