Next Meeting
Agenda for Next Meeting
Item Person Responsible Time ---- ------------------ -------- Status of Open Action Items All 5 min Commissioning Schedule Bohn 15 min Status of Diagnostic Procedures Piot 30 min New Issues All 5 min
This Week's Attendees
S.Benson, G. Biallas, C. Bohn, J. Boyce, A. Hofler, K. Jordan, R. Li, L. Merminga, G. Neil, D. Oepts, B. Yunn
Closed Action Items
Items of Discussion
Commissioning with beam resumed Monday, 1 Jun 98. Activities have centered on developing a solid injector setup and firming up techniques and procedures for measuring transverse emittance. One of the Happek interferometric bunch-length monitors is installed for fit-up, and the other was tested off-line this week with very encouraging results. Next week we plan to begin testing it with beam. On the positive side, we found this week that it has been easy to run 1.1 mA cw beam in the accelerator, which we did on two occasions for a total of about an hour. The first was to see what difficulties would arise, and the second was to recalibrate the beam-current-monitor cavity. Prior to the first mA run, we ran 0.6 mA for several hours to check cathode lifetime, and it changed imperceptibly during that run. However, on the negative side, the cathode degraded substantially during owl shift this (Friday) morning, apparently in association with a brief surge in the gun current that occurred during pulsed-beam operation. Presently, our plan is to recesiate the cathode on Monday, 8 Jun 98, and check it then. Today we are able to get close to 60 pC bunch charge and are continuing injector setup.
Injector setup has been hampered by some technical difficulties. First, we continue to see substantial changes in what appears to be the rf phase of the drive laser, and the drifting makes it difficult to phase the accelerating cavities. We subsequently instrumented areas in the vicinity of the cabling associated with the drive-laser rf system for thermometry, but have not seen any inordinate temperature fluctuations. This finding, combined with checks done during our recent down time, means we still do not know what is causing the drift. Second, we set forth last night to calibrate the gradient of the buncher cavity that precedes the cryounit following a procedure that centers on bunch-length measurements with the first M_55 cavity, but we were stopped by a failure of the calibration routine for the M_55 cavity. The problem is being investigated today.
Our priority effort at this time is to calibrate the gradients of the cryounit cavities. Per the control screen, they are presently at their nominal settings, for which the output momentum should be 9.99 MeV/c. The injection-line dipole string is now set to 9.12 MeV/c momentum, about 8% low. This detail is a potentially important one insofar as it might influence calculated beam properties, i.e., PARMELA simulations. The effect on the simulation results is presently under study.
Progress on emittance measurements has been slow but steady. Measurements of emittance at the cryounit exit with Multislit #1 give a normalized emittance of about 5.5 mm-mrad. A preliminary analysis of data taken with the multimonitor and quad/viewer techniques indicate an emittance at the wiggler location of about 6-7 mm-mrad, less than the target value of 9 mm-mrad. These measurements were slowed by ghost-pulse saturation of key viewers. Last night it was found that the analyzer polarizer at the output of the second electro-optic cell had been photorefractively damaged. The polarizer was replaced, and the ghost-pulse problem appears to be solved. In addition, two of the cameras were falling in and out of beam sync, inhibiting the quad/viewer measurements, and these cameras will be diagnosed Monday.
Concerning other progress on "Subsidiary Tasks for Phase Space Metaprocedure", we have obtained agreement between the energy-fixed-point and transient-phasing methods for setting the rf phase of the buncher cavity. The remaining subsidiary tasks are listed at the end of these minutes in the format of the original outline.
G. Krafft presented a synopsis of the Happek device and how it works. In essence, it converts optical transition radiation from a foil into an interferogram that is a convolution of the electromagnetic fields impinging on the mirrors of the interferometer. A Fourier transform of the interferogram generates the electromagnetic spectrum, which in turn is proportional to the bunch form factor. Consequently, there is a direct relationship between the interferogram and the bunch length. Off-line testing of one of the Happek devices indicates that the mechanical movement of the mirrors checks out, and the detector (Golay cell) works well. This device will be swapped on Monday with the second one (already in place for fitup). The former will be tested with beam next week, and the second will be tested off-line. Once the device is optimized, it will generate a bunch length in less than 10 minutes. We need empirically to determine the beam mode necessary for its operation, but the performance of the Golay cell implies it may be operable with our standard viewer-limited beam. We shall soon see. Krafft and K. Jordan also reported that a pyroelectric detector has been successfully checked off-line, and it will be installed Monday at a synchrotron light port to monitor coherent synchrotron radiation at that port, thereby enabling a cross-check of the Happek device.
C. Bohn advised that he wishes to keep tidy the FEL console in the MCC. He noted that the FEL binder is now quite messy, making procedures and test plans hard to find. He is putting together a well-organized binder and, once it is complete, he will have it replicated and placed in the MCC so that the procedures and test plans are kept separate from other FEL documentation in the control room. Bohn has copies of all current procedures and test plans accessible from www, and he asked that individuals who have not yet posted their documents to do so and give him a copy by COB Monday. He also asked that they all be put in the standard JLab template. We need to stay professional in our work.
K. Jordan and G. Neil reported that the Optical Control Room is very nearly ready for first light. Still missing are an x-term and a workstation, and Jordan is working with K. White to get them installed soon.
The general pattern of daily commissioning activities for the next two weeks will nominally be: Day Shift working through the Metaprocedure, Swing Shift checking out diagnostics and exercising the machine, and Owl Shift measuring beam quality. Bohn and Neil will work together during the day shifts to try to catalyze the setup of the machine per the Metaprocedure and will bring people in to the control room as necessary to speed things along. With Bohn being in the control room, J. Fugitt's role as Experiment Coordinator will be a more visible one in that he will be functioning more like a Program Deputy. Formal staffing for the next two weeks, modulo some localized excursions already known to those affected, is:
8-12 Jun 98: Owls - Hill, Piot ("standby"), 1 CEBAF operator
Days - Bohn, Neil (standby), 1 CEBAF operator
Swings - Oepts, Krafft (standby), 1 CEBAF operator
1-5 Jun 98: Owls -- Evans, Piot ("standby"), 1 CEBAF operator
Days - Neil , Bohn (standby), 1 CEBAF operator
Swings - Shinn, Krafft (standby), 1 CEBAF operator
(Note: The FEL two-week schedule has for some time been accessible via www
from either the FLOG page or the FEL Documentation Page, and it is updated
frequently.)
New Issues
None.
New Action Items
Old Action Items
Test Plans in Work
Procedures in Work
Emittance Growth from CSR
Procedures Needed for Recirculation
Unfinished Subsidiary Tasks for Phase Space Metaprocedure
Task Principal
---- ---------
I. Stabilize Drifts in Drive-Laser RF Phase Walker/Fugitt
II. Calibrate RF Gradients
A. Buncher Yunn
B. Cryounit Cavities Merminga/Krafft/Yunn
C. Cryomodule Cavities Merminga/Krafft/Yunn
III. Reconcile Methods for Setting RF Phase Merminga/Krafft/Yunn
A. Buncher Cavities
2. Minimum bunch length/time of flight
B. Cryounit Cavities
1. Transient phasing
2. Cresting
3. Time of flight
V. Finalize "Injector Setup" Procedure Yunn/Biallas
F. Emittance at Wiggler, 2G02 (with Li)
G. Momentum Spread at Wiggler, 2G02 (with Li)
IX. Complete Diagnostics Procedures and Training Krafft/Piot
A. M_55 #1, #2
B. Happek #1, #2
C. BPMs
1. button calibration factors
2. rotated MEDM spike charts
3. difference orbit data acquisition script
D. Multislit #1, #2
E. Quad/Viewer (at Wiggler, after Wiggler)
F. Multimonitor (at Wiggler)
G. SLM/CSR
H. Zero Phasing
I. Momentum Spread (Injector, Linac Pre-Wiggler, Linac Post-Wiggler)
J. Energy
X. Develop "Injector Rematch" Procedure Biallas/(Unk. Physicist)
XIV. Update (as appropriate) "First Light" Procedure Benson