Accelerator Test Facility

The STELLA group, including Wayne Kimura & Christian Dilley from STI, concluded another full week of running the dual-wiggler experiment on beamline #1. Recall, the first permanent-magnet wiggler in line acts as a prebuncher while the second (currently in the place of the ICA cell “location #2”) serves as the accelerator section. Once again, the goal was to observe bunching and trapping of the electron beam.

Initially, there was difficulty in reestablishing appropriate modulation in the second wiggler. Numerous variables in the system were checked and the problem was narrowed down to the wiggler itself. The #2 wiggler was installed into the wiggler #1 location to confirm proper operation at the expected resonant energy (~46.5MeV) and the nominal 45.6 MeV beam energy. To optimize resonance at location #2, the gap was opened by removing ~7 mils of shimming.

Individual and joint wiggler synchronization was established and optimized via rough delay stage scanning. Laser delivery to both wigglers was checked for optimum transmission, and fine steering mirrors were scanned to maximize modulation. Fine delay stage increments (~1.2 microns on the accelerator section only) varied the relative phase overlap between the two wigglers, which qualitatively showed some degree of control over the electron bunches. A few of the spectra taken are shown in the hyperlink below. The spectra shown are for approximately the same laser power, and are as follows: (1) laser off, (2) laser on IFEL2 only, (3) and (4), a pair at the same optical delay (readout with arbitrary zero at 25.2 microns), (5) and (6) a pair of shots at a delay of 30.0 microns (stage moved about 5 microns from previous pair), (7) and (8) at 32.4 microns (about 2.4 microns, or 2.4/10.6 of a laser period).

5_19_STELLA_spectra.htm

Note that the spectra for the same delay value are reasonably similar, indicating a reasonable phase stability in an optical linac regime.

It has been frequently observed that the modulation effect in wiggler #2 was very sensitive to electron beam energy, tuning, and stability. However, the primary limitation to the maximum extent of modulation seems to be the laser power delivered to wiggler #2. Therefore, efforts over the next few weeks at ATF will focus upon improving laser transmission through the wigglers, further minimizing optical transport losses, and possibly increasing laser output. At STI, the team will continue with wiggler simulations (gap vs. energy, etc.) and data/image analysis.

Preliminary comparisons with the recent data and the model are encouraging. It is hoped that this will reveal clear evidence of trapping and acceleration of the microbunches

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VISA Experiment (REPORTED BY AARON TREMAINE)

These last two weeks were shutdown for VISA. Pedro made a special trip out to help with the shutdown assembly, fiducialization, and insertion of the pop-ins and Don was relieved from general ATF duty and dedicated to VISA for the shutdown.

Robert came out and did an interferometric alignment and the undulator was aligned to a precision better than 10 microns. The red alignment laser has been positioned and is aligned to the magnetic center axis to better than 50 microns with drift. The 800 nm alignment laser broke and has been sent to Melles Griot for repair and will hopefully be back by the beginning of June.

The ATF has loaned us a small actuator and a Pop-in has been installed at the first port so we will have all 8 BPM monitors for the remainder of the experiment.

Also, view ports/camera monitors have been added to the system to allow monitoring of the VISA undulator while under vacuum. There are 5 positions for horizontal movements that are being monitored: the front section 1, between sections 1&2, 2&3, 3&4, and the end of section 4. We have started pumping down and observed the joint between sections 3&4 move. Upon looking at all the pre-pump and post pump snapshots taken, the undulator does appear to move when pumped down. I will have more quantitative data at tomorrows meeting.

The posted Web schedule has a run day for May 23 but this was traded with the fast detector for an extra run day before the shutdown which turned out well for us. Our next run days are scheduled for May 30,31. These will mostly be debugging the system and returning to where we left off.

This week the system needs to be prepared for the run days next week: Mount/wire up steering magnets, hook up airlines.

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Technical Operations (REPORTED BY BILL CAHILL)

Coming out of the maintenance period and into operations went pretty smoothly. The cable assembly that operates the transport plug door was replaced by Bob Harrington and works better than ever. Modifications were made to enhance the wire cable layout and overall safety of the unit. Extensive work has gone into the YAG temperature control system and it will be installed this weekend. The Linac water temperature control system is coming along nicely and appears to be on schedule. NSLS electrician’s will install the needed power for the new chiller associated with the Gun solenoid on Monday along with new power for the Linac temperature control system. Efforts are being made to occupy the new offices in bldg. 820M. The custodial crew should have the spaces cleaned by the end of the week and be ready for occupancy. The Terawatt laser vessel will be pressure tested this weekend and be returned to the ATF for installation on Monday. Electrical control problems have plagued the a/c system for the Experiment hall and CO2 laser areas. Crews are on hand to normalize the system and maintain stability. Aside from various speed bumps, the technical staff continues to support operations on a daily basis.

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Friday Engineering Meeting(REPORTED BY XIJIE WANG)

Week ended May 12:

1. ATF improvements: this week more RF maintenance was done, new metal case capacitors installed for testing. All looks good.

2. Linac and Laser water system status: due to delay of parts to be delivered, neither system was ready for installation this week. We hope to complete both systems next week.

3. Limit switch for CO2 delay line: Mark will work with Karl on the delay once linac water system finished.

4. New magnet power supply: we decided to build a 24 channel, 30 A power supply over the next few months.

5. TW CO2 laser discharge cell: Igor reported that the cell will be ready return to ATF by the end of next week after testing, I requested moving the cell during the Monday maintainance day to avoid interference with experiments. Cahill should prepare a work order for the moving next Monday first thing.

6. Next Monday afternoon, starts at 2:00 PM, every hour, we will have ATF operator and duty operator on-hand training.

Please submit your experimental running time request, from June 12 to the end of August by next Wednesday.

Week ended May 19:

1. Next Monday maintenance jobs: install chiller for gun solenoid and fix the gun vacuum valve.

2. YAG laser: Harrington will install new water system this weekend on overtime so laser system will be ready next Monday for operation. Marcus need to work on the laser profile next Monday.

3. TW CO2 laser: discharge cell will be back next Monday. Starting Tuesday , both Harrington and Don will work on the assembly of the TW CO2 laser.

4. HGHG: Harrington and I have modified Ipop2 into a transition radiation monitor with CO2 transmission window.

5. VISA will be ready for vacuum pumping this week-end.

6. Bill is arranging Janitorial service for the ATF user meeting.

7. People should register for ATF user meeting on June 1 and 2 with Kathy Tuohy.

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Last Modified: December 3, 2007
Please forward all questions about this site to: Vitaly Yakimenko