Contents
1. Introduction	4. Photoinjector
2. VISA	5. YAG System
3. Facility

In the period since last report we have been busy with PAC’99 and the ICFA Meeting on Future Light Sources. As always, many thanks to all contributors to the report. I have added a few names (mostly users) to the distribution list. If any of the newly added addressees would like to receive ‘back issues’ of this report, please write to me.

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EXPERIMENTS:

VISA

VISA Magnetic measurements (Reported by George Rakowsky):

Undulator Sections #2 and #3 were checked on the pulsed wire bench. After some adjustments, a satisfactory X and Y trajectory was obtained in both sections as seen in the image at: VISA_Sections_2_3 (The apparent slope in the trajectory exiting Section #3 is not an error. In fact, Section #3 is well-matched to Section #4, which is absent from this measurement.)

Section #1 arrived back from SLAC after rebuilding, with the prototype laminated gap spacer assemblies replaced with the same one-piece spacers used in Sections 2, 3 and 4. Next week Section #1 will be remeasured and retrimmed and will be matched with Section #2. The steering magnets arrived from UCLA. We are planning to set up four of them on the pulsed wire bench to calibrate them for Earth’s field compensation. This will be done in late April, after completion of the undulator measurements.

Jeff Aspenleiter has completed the automation of R. Ruland’s procedure for interferometric measurement of the tooling ball offsets on VISA. This project included designing and building a control circuit to interface the DC motor on the straightness interferometer stage to the computer. He also developed a LabView program for sequencing the positioning of the stage, reading the interferometer, averaging the readings, and performing a circle fit to the data to find the true offset of the fiducial. This will greatly speed up the interferometric calibration of the VISA magnet sections and the final alignment at the ATF. Good work, Jeff!

A paper on VISA magnetic measurements has been presented at PAC99.

Following PAC, t============================== rajectory trimming of Sections #1 and #2 together has been completed. Robert Ruland was here for three days this week. He brought the rebuilt wire finders with him. They are now repeatable to <1 microns. We measured the fiducials of Sections 1 and 2 with the straightness interferometer. Measurements were done with the magnets in normal and inverted orientation. The repeatability of measurements at each fiducial appears to be on the order of 5 microns rms. Robert still has to reduce the data, with reference to the CMM data from SLAC.

I attended the ICFA Future Light Sources Workshop at Argonne last week and gave a talk on the VISA undulator. It seemed to have been well received.

VISA Optics (reported by Alex Murokh):

The design is completed by Erik Johnson. The first mirror will be shipped to UCLA for polishing by Monday next week. The complete prototype will be build at a BNL shop in two weeks. If all goes well all the probes will be ready in the mid-May Then, the probes will be tested and connected to the feed-throughs. Hence, if there will be no major drawbacks, the complete installation of seven diagnostics ports can be performed in the mid-June.

It is ordered. Initial testing will be done at UCLA (and maybe SLAC). It can be shipped to BNL in mid-May. The mounting will be designed by the end of April.

The cameras are ordered (Hitachi KP-M3). The choice of lenses and a complete system layout will be finalized by the end of this week. All the components should be available for installation in May.

Flippers will be ordered this week. A complete design will be finalized next week. Will be ready to install at the end of May.

The systems above require fair amount of control. The details will be discussed within next few weeks. Hopefully, the experimental schedule will stay unaffected, as the control system can be worked out in parallel with the hardware.

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Facility

TECHNICAL STAFF TASKS (reported by Bill Cahill):

The following items were accomplished during the week of April 26.1999.

1. HPOP-1.5 was installed.

2. Phosphor screen for LPOP-1 was completed.

3. High voltage grounding solenoid was installed in linac modulator.

4. Arc detection circuit was installed in linac modulator. This device senses a drop in charging voltage cross the pfn to detect and interrupt operation in case of arcing.

5. Prep YAG clean room for HVAC renovation.

6. New YAG chiller was installed, HEPA filtration system regasketed, speed controls added, hard insulation installed over new and existing duct work, a/c rerouted into gun hutch and machine shop a/c duct removed.

7. Beamline #3 vacuum system disconnected downstream of manual valve, all connections disassembled, faraday cup assembly nitrogen back-filled and capped off for VISA experiment installation.

8. VISA electrical cabling being installed, approximately 85 runs.

9. Facility in clean-up mode for PAC Tour.

The following is a list of technical accomplishments for the week of 4/5/99.

1. All requested cables for the VISA Exp. have been pulled.

2. The IFEL wiggler has been installed in beamline #1.

3. The Compton Experiment has been removed.

4. STELLA spectrometer reinstalled.

5. STELLA faraday cup shielding built and awaiting approval.

6. Arc detector system installed in both modulators and operational.

7. All components downstream of D4 on beamline #3 have been removed.

8. X.J.Wang and Bob Harrington changing cathode in electron gun.

The following is a list of technical accomplishments during the week of 4/12/99.

1. Cleaning of YAG laser room following last weeks construction.

2. Fabricated new shutter for test oscillator, mounted HEPA filter.

3. Relocated video multiplexer and added 16 new channels to accommodate the VISA Experiment. Removed all ‘illegal’ coax cables associated with the video system.

4. Eliminate rad waste, "Krytron tubes" used in laser system.

5. Order parts for Strip-line Monitor system.

6. Re-certify laser security system.

7. Submit permit for certification on STELLA faraday cup shielding.

8. Begin design work on Klystron cooling enclosure.

 

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Photoinjector (Reported by Xijie Wang):

The cathode of the RF gun was changed to inspect the surface of the old cathode and change to a new cathode. The magnesium cathode taken out of the gun was inspected by Triveni Srinivasan-Rao. We were able to find two craters on the cathode with a diameter of about 100 microns and a depth of 0.0006 inch. Comparing a copper cathode taken out two years ago, the copper cathode has many more craters at depths of about 0.0004 inch. We will start preparing the magnesium cathode which was taken out next week, once we receive the cleaning agent. Photographs of the replaced magnesium cathode and the old copper cathode are shown at atf_cathode The damage conditions are very similar for the two cathodes. We know from previous experiment that no double pulse was observed for the copper cathode. We were be able to operate the ATF RF gun at 24 C today. After 3 hours of conditioning we reached a field of 70 to 80 MV/m. We will resume the conditioning next Monday. We are planning to test the cathode next Tuesday afternoon.

CO2 laser (Reported by Igor Pogorelsky):

Modification of the CO2 slicing from 200 ps to 10-7 ps is under way.

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YAG System

Temperature monitoring (reported by Vitaly Yakimenko):

A system of 11 thermocouple was installed to monitor the temperature in a few locations in the Yag room. The thermocouples were calibrated to provide identification of temperature fluctuations and variation from one location to another with an accuracy of about 0.2 degree C. The system is running and collecting data. The initial data shows fluctuation in temperature of 1.5 - 2 degrees C (peak-to-peak). More detailed information will be available next week. That amplitude is in agreement with data measured by original temperature control system.

New Oscillator Mode Measurement (Reported by Adnan Doyuran):

I measured the beam size at different positions. While Y kept diverging, X gave a focus after 4m. We made a Gaussian fit to this beam and found the parameters of the beam using Mathcad. The result is in a pretty good agreement with the measurement. Then using Beamcad we calculated the optics and found out that we need a +2m focal length cylindrical lens for the Y direction and for beam matching we need a -1m lens. These have been ordered on Thursday.

Laser (Reported by Marcus Babzien):

There has been no laser operation for two weeks due to the HVAC work on the clean room. The new chiller is now in place, and ductwork, insulation, HEPA fan controllers, and fireproofing have been added or modified to continue to improve performance of the HVAC system and meet safety requirements. The HVAC shutdown progressed enough last week to allow work to begin in the YAG room. We expect that the climate control will be better able to prevent high humidity in the room, and that there has been some reduction in vibration. Temperature monitoring and vibration measurements will show if these parameters are now within acceptable limits, but observations so far indicate that they are not and further effort will be required. Some final work in the ceiling plenum was completed by Tuesday, and then extensive cleaning was performed to restore clean room conditions. The electronic equipment previously moved for the shutdown was reconnected and all cabling restored. Thermocouples for more careful temperature measurements were installed and are now being recorded on an additional PC installed in the YAG room. This PC is also able to recall HVAC data recorded by Plant Engineering.

Preparations for the testing of the new oscillator also began this week. The first test will be to illuminate the photocathode if possible and check the beam quality. To accomplish this quickly, the mode of the output beam was characterized, and mode matching optics purchased. The transport and matching optics are being installed to enable quick changeover between seeding with the old oscillator and the new one. If the new oscillator amplifies well, a test beam may be available as soon as Tuesday afternoon.

SCHEDULE (reported by Xijie Wang):

Klystron thermal insulation: John Skaritka presented an overall outline design of the insulation. The detailed design will be finished next Friday. Bill Cahill will order parts soon, and John will arrange a meeting with plant engineering to plan for the installation.

Noise problem. Marc Montemagno suggested that the source of most of the ATF electromagnetic noise may be the gun klystron power supply SCR. Vitaly proposed to borrow a power supply from the NSLS to test if this is true. If so, the ATF should proceed to purchase a new power supply.

ATF Schedule:

There is a great uncertainty in the ATF schedule due to the on-going YAG laser work, so the main work next week will be:

1. Beam tests: Tuesday

2. If he newly installed cathode is not satisfactory, we may want to change cathodes again on Thursday.

3. YAG laser work all week.

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