Next Meeting

Date: 15 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

J. Bennett, S. Benson, C. Bohn, J. Boyce, D. Douglas, F. Dylla, J. Fugitt, A. Hofler, C. Hovater, R. Lauze, R. Li, L. Merminga, G. Neil, M. Shinn, Q.-S. Shu, T. Siggins, R. Walker, B. Yunn

Closed Action Items

• Walker/Bohn: Ascertain need and develop guidance for routine checks of arc detectors and BLMs.
  Status: Operators have been instructed to test BLMs and check cryounit arc detectors once per shift. G. Lahti is scheduled Monday, 11 May 98, to upgrade software to automate checks of the arc detectors.

Items of Discussion

This week's activities centered on continued commissioning of diagnostics, including development of procedures to use them, additional difference-orbit measurements, and developing a reproducible injector-setup procedure that involves diagnostics downstream of the injector. None of these activities are complete yet, but progress was made in all of them. In addition, one shift was used to devise a BLM setup that would permit operating the Happek interferometric bunch-length monitors as well as to recheck the BLM settings for cw running. Regarding the latter, the voltage of the BLM at the straight-ahead dump was adjusted, but otherwise the existing setup looked appropriate.

One complication is a persistent drift in the rf phase of the drive laser that began to be observable about two weeks ago. The drift causes the beam properties to change concomitantly, and it must be eliminated prior to trying to lase. We believe that it was introduced as a consequence of some hardware changes in the drive-laser rf system, and we have been trying to track down the cause using well-defined test plans. At this writing (1115, 8 May 98) we still had not done so definitively, but we have suspected causes that we will check over the next few days.

C. Bohn summarized the status of the electron-beam diagnostics as follows:

• MaxVideo works for beam size measurements. However, on several of the viewers noise and dead pixels prevent its use because the signal-to-noise ratio is too low.
• Current monitor cavity works and is in constant use.
• BPMs work; 2 cans (1 injection line, 1 linac) are bad but can reproduce orbits. One of the bad cans is the key BPM in front of the wiggler, and it needs to be replaced to enable setup for lasing. Replacement is scheduled to occur tomorrow (Saturday). We don't yet know whether the BPMs have the resolution or stability needed for FEL setup.
• Multislits work, including analysis software; we are deciding on the best way to use them. Neither of the multislits presently gives an emittance measurement in the standard beam setup. It may be possible to get the needed measurements by altering quad settings and then backing out the numbers, and we are presently working on the methodology for doing so.
• Quad/viewer works; we need the final setup for good numbers. One complication is that we may need to turn off the raster magnets at the straight-ahead dump to use the last viewer. The overall procedure is not yet finalized, but it is in process of being developed.
• Multimonitor works, but the uncertainty in the measurements is presently too large (±50%) for the data to be useful. More refinement is needed.
• M_55 cavities work as bunch-length monitors; the associated software has been checked.
• Zero phasing works, but we need good steering through the cryomodule cavities to get good data. There is presently no approach that is reproducible operator to operator at the needed accuracy, so work on the technique continues.
• Happek is scheduled to be here from 10-13 May 98. We will install his hardware during day shift Monday and test it during swing and owl shifts Monday and Tuesday nights next week.

G. Neil reported that significant progress was made toward setting up the FEL optical systems. Optical transport diagnostics were completed, aligned and put under vacuum, and they were used to take a surrogate HeNe beam from the FEL to the diagnostics table in the optical control room. Patch panels to the optical control room were installed and fully wired. Fiducialization of the first-light mirrors was completed. The mirror-control software for save/restore was verified. The cavity mirror alignment as viewed through position sensors drifted by less than 10 µrad over several days, well within specification.

More discussion about the always popular topic of configuration control arose. D. Douglas pointed out that he has difficulty iterating toward an optimal orbit when the machine setup keeps changing. Bohn reviewed the configuration control policies instituted to date, reiterated that the present Golden File is Douglas's file from last Wednesday, and explained once again how the planned shift activities are designed to converge on a usable setup for lasing. The process should get easier, and the procedures should get firmer, once the machine is "complete", meaning to zeroth order that the Happek monitors are installed and checked out, and that is scheduled for the beginning of next week. Bohn is totally open to ideas on how to do things better and more efficiently. He also will soon convene a meeting to discuss elements of the procedure for setting up the longitudinal phase space.

R. Lauze asked that we prepare a glossary of FEL terminology as an aid to CEBAF operators. New hires should be showing up soon, and they will benefit from this head start. R. Walker will begin compiling the glossary.

M. Shinn presented a synopsis of measurements of drive-laser noise. Her principal observations are:

• The drive laser performs best when running on its internal rf system. Performance is comparable to the required value for (FEL) lasing: <3% p-p at 10 Hz > f > 50 kHz, but worse than measured when the laser was new (1.3% p-p on 3/30/95).
• When running on external rf, amplitude noise is higher. Closing the phase-locked loop results in amplitude noise of order 18-19%. This needs to be fixed.
• The electro-optic cells do not contribute to the amplitude noise.
• Beam scraping on the optical-transport aperture increases amplitude noise by about 25%.

• Determine causes of degraded laser performance on internal rf and fix.
• Determine why the rf control system causes increased amplitude instability and fix.
• Add a "noise eater" after the EO cells (preferably after the aperture). One is available already, but it would decrease the maximum laser output to 5 W.

Over the next two weeks the basic program is to do orbit and phase-space optimization during day shifts, cw runs during swing shifts, and beam diagnostics/beam quality measurements during owl shifts. Progress from each shift will feed into the other shifts as together we iterate toward a usable lasing setup. Shift assignments for the next two weeks are (remember to use the CEBAF operator!):

11-15 May 1998:

Owl -- Merminga, CEBAF operator, Piot on standby

Day -- Douglas, CEBAF operator, Benson on standby

Swing -- Shinn, CEBAF operator, Siggins on standby (Krafft also on standby for Happek checks on 11-12 May)

18-22 May 1998:

Owl -- Walker, CEBAF operator, Piot on standby

Day -- Bohn, CEBAF operator, Neil on standby

Swing -- Siggins, CEBAF operator, Hill on standby

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.

 
Measure Beam Stability                     Benson, 15 May 98
    (dE/E, dx, dy, dx', dy')

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

Tomographic Phase-Space Map                 Piot, 30 June 98
Back Leg Thread                             Douglas, 30 June 98




Procedures Needed for Recirculation


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