Contents
1. Introduction	6. Computer and Control
2. HGHG	7. YAG Laser
3. STELLA	8. Accelerator Operations
4. VISA	9. Operations Schedule
5. Compton

 

Greetings all,

This week we had runs of the STELLA experiment and HGHG. Good progress in both experiments. HGHG started the seeding by injecting a CO2 beam and observing the energy modulation produced by the modulator wiggler. STELLA is continuing to reduce the beam size in the interaction region of the Inverse Cerenkov Accelerator.

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****EXPERIMENTS:***************

 

HGHG Experiment (Reported by Li-Hua Yu, Xijie Wang and John Skaritka)

Run results:

Thursday and Friday we managed to synchronize the CO2 laser with the electron beam and create a huge energy modulation. Following a reduction in the CO2 power by a factor of 30 the modulation magnitude was measurable. The modulation width in time was measured by varying the time delay in the CO2 beam to measure the CO2 pulse shape. This will be used to calibrate the CO2 power. This is an important step forward, being the beginning of seeding. The next step will be High Gain Harmonic Generation.

The images taken (for the case of the low CO2 power) at the spectrometer in

the end of the HGHG beam line (ATF Beam Line 2) are in the

 

_modulation_in_HGHG.htm

Mechanical work:

1.The micro bunch detector table with optics holder was installed into beamline 2.

2. The pyro-camera camera mount needed for the spectrometer in the FEL room was designed, fabricated, assembled, and installed on time as requested.

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STELLA Experiment (Reported by Karl Kusche)

1) The results from our last beam studies run were reported - the best focus achieved at GPOP5 with the IFEL wiggler & ICA gas cell removed was ~120x72 microns (with 300x300 microns at GPOP4). Intuitively, we should expect an even smaller focus at the actual interaction region (which is ~20cm upstream of GPOP5). Vitaly requests that further beam studies and iterations with simulations be done during next week’s running time (instead of running ICA), and that verification/improvements of GPOP4&5 resolutions be done. It was also requested that Ping process the images of all pop-ins saved during the best tune.

2) Pursuant to the previous item, we will utilize the 3-day running period (8/9-8/11) in part for beam studies with an iris placed in the beam path at the interaction region to check the resulting beam quality. If this method is deemed useful to reducing spot size, we may try to use an axicon mirror (or laser shield) with a smaller hole to act as the beam iris in the future. 3) Other items: Wayne introduced the idea of using an encoder-mike stage in the gas cell to more accurately place the wire cross diagnostic for laser/e-beam alignment. He also mentioned the possibility of ordering a new axicon mirror with reduced apex angle (10 mrad) to allow for increased laser spot size at the gas cell.

Revised STELLA schedule:

• This week = install/survey ICA gas cell, remove cell mirrors, check iris position/mounting.
• Monday (8/9) = (AM) Tune through gas cell; (PM) Iris tests: 275 & 100 micron holes.
• Tuesday (8/10) = Install ICA cell mirrors, reestablish & optimize tune.
• Wednesday (8/11) = Finish tuning.
• Week of August 23 = Tests of cell diagnostics (VOx target, wire cross,etc.)

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VISA Experiment (Reported by Aaron Tremaine and George Rakowsky)

 

We need a new chiller for the 30 A power supplies required for VISA. Due to the fact that the ATF ran out of funding for FY99, a serious delay is expected in full energy VISA operations.

Robert Ruland and Brian Fuss completed their working visit on Tuesday. Due to various mechanical problems (loss of 3 fiducials, jammed kinematic adjusters, lack of lifting or guiding fixtures for inserting the magnets into the chambers) and unavailability of key people (Jeff was called to repair a VUV cavity) during the previous week, they were unable to do a full "dress rehearsal" alignment. They were, however, able to do a trial alignment measurement with the interferometers, once on Friday before pumpdown and again on Monday after venting to atmosphere. Measurements on most of the fiducials agreed to within 5 microns. A few had large errors, but the source is understood and fixable. This means that the magnets and vacuum chamber are indeed decoupled and the magnets did not creep when cycled to vacuum and back. The other good news is that the chamber with the 4 magnets pumped down OK. A small leak was found at a side port due to a scratch on the sealing surface. Jeff polished it and now it seals OK. The vacuum chamber and undulator were pumped down with a 125 l/s turbo and reached 10^-5 in 12 hrs.

A pop-in assembly was test fitted in one of the diagnostic ports and centered so it does not touch the magnet over its full range of motion. Contact was checked electrically by isolating the pop-in assembly from the chamber. The test was repeated with the chamber evacuated. There is no contact, except at extremes of travel. John believes this will not be a problem. The other seven pop-ins parts are made and assembly of them will begin soon. We are still waiting for results on the mirror polishing which should come in a few weeks.

The VISA magnets and wire finders will be shipped back to SLAC to have improved tooling ball assemblies installed. Higher accuracy ceramic balls with diameters matched to 25 microinches (0.6 micron) will be used on all magnets and finders to reduce systematic errors. Then everything will be remeasured on SLAC’s CMM. This will result in approximately 4 more weeks delay.

A "pseudo" beamline is installed in beamline 3 (where VISA will go) in the ATF. In early September, beam will be run through this beamline and debugging of the diagnostics and beam transport will be done. This will help in the initial startup of VISA.

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Compton Experiment (Reported by Shigeru Kashiwagi)

       1. VOx target

We tried to observe the CO2 spot on the VOx target at the test bench and we succeeded to make a spot on the target using not-coaxial beam. (I had many suggestions and help form Karl.)

At first, we observed the CO2 spot on the VOx surface directly. We can control the density of CO2 spot by changing the target temperature. Then spot size was about 400 micron (full width = 4 sigma). Then target was not damaged. (laser energy : 30mJ , Attenuator : ½.43, 1/3.6, 1/13.5, Target temp : 43 -- 59C)

Next, the CO2 illuminated the back surface of VOx target, and the laser spot was observed from the other side (that of the VOx surface). The CO2 laser spot size depended on the laser power. At some high setting the target sustained some minimal optical damage.

Laser energy Att. Spot size [um] (full width) Target temp.

26.4mJ (13.5/3.6/2.4) no spot 53 C

25.4mJ (3.6/2.4) 270 53 C

27.1mJ (3.6) 750 53 C

25.3mJ (2.4) 1000 53 C

23.9mJ (no) 2250 53 C

2. Pico motor

We inserted the leaf spring (made by Bob Harrington) below the Cu mirror to support the weight of mirror. With this modification, the mirror drive system was improved and the motion is hysteresis-free.

3. X-ray Detector

We will try the calibration for our detector in an NSLS beam line. I have asked Dr. Kao about his beam line schedule. He will tell me our beam time on 8/6. I am also investigating other photodiode detectors.

4.BPM

We will try to measure pulse-to-pulse beam orbit using strip line type BPM and measure a correlation between X-ray signal and e-beam orbit. I borrowed the electric circuits (ADC, 1-shot generator, clipping circuit) from KEK-ATF. I will test these circuits. In this week, I already ordered the cable for this measurement.

5.Calculation

I calculated the number of generated photon for some different cases.

A typical example: Electron beam charge 0.5 nC, electron beam emittance 2 mm mrad (normalized), laser peak power 0.5GW, Laser energy 0.038 Joule, then the luminosity is 3300 (1/mb) and the number of x-ray photons 2E6. (Number of photon = Cross section (compton) x Luminosity, (Cross section = 665mb)

Assumptions:

Beta(x) = Beta(y) = 1 [m] at waist point

Laser spot sig_lx = sig_ly = 100 [micron], sig_lz = 22.9 [mm]

Laser energy [J/pulse] = Peak power [W] x sig_z l[s]

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****FACILITY:**********

Computer and Control System (Reported by Bob Malone)

New ATF control system development effort:

1) Vista Control Systems has received our purchase requisition for new Vsystem software licenses. This new software will form the basis for ATF’s next generation control system which operate under Linux on Intel PC hardware.

Vista will ship the final media and license keys sometime in the next 2 weeks. In the meantime, we have a temporary beta kit, 10 volumes of documentation and a license key which is valid until the end of August. 2) Using the beta kit/temporary license and an old spare (slow) 133 MHz PC, work was started on assembling a software development system. Linux and Vsystem were installed early in the week and testing began Wednesday. Some problems were uncovered which related mainly to incompatible versions of run-time libraries. Vista responded to our support request within 1 hour of receiving it, but had extreme difficulty in communicating the fix due to the unreliability of BNL’s e-mail service during the "hacker crisis." Things cleared up on Friday and we should have the fix in place early next week.

Using this development system, intensive testing will continue for the next several months. We plan to identify and (hopefully) solve any problems which relate to porting the present ATF control system to the new platform. Experience gained in these small-scale tests will be invaluable once we begin the very large task of migrating the entire control system. New Ethernet CAMAC crate controllers will be purchased early next fiscal year and will be incorporated into the test/development system to help resolve hardware porting issues.

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YAG Laser Operations (Reported by Marcus Babzien)

Tuesday and Wednesday were devoted to maintenance. The Pockels cell installed last week with the new high voltage pulser for double pulse operation was optically damaged. To continue double pulse operation, the previously used Pockels cell needed extensive mechanical work to function with the new pulser. This took two days to complete, but double pulse operation was restored late Wednesday. The Pockels cell now in place was exposed to the same beam conditions for two weeks without suffering damage, and should be reliable.

Thursday morning during the HGHG run the new oscillator power drop observed steadily over the past two weeks accelerated and modelocking finally became unstable, leaving the system inoperable. The oscillator cavity was adjusted to restore proper modelocking, maximize power, and achieve best mode. After thermal equilibrium was reached that night the system was realigned and operation resumed.

Monday and Friday operation was uninterrupted.

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Accelerator Operations (reported by Xijie Wang)

1. ATF Schedule for September and October: The only request received so far is from the Compton experiment. The tentative schedule will be announced next Friday. We have tentatively set down the following time for two ATF shutdown, as detailed below: (Additional tasks will be added later)

A. Week of August 27 - September 7, 1999. The tasks for this shutdown are:

1). Install Compton experiment

2).Install VISA test beam line

3). Pull additional cables for VISA

4) Switch quadrupole magnets power supplies for VISA 70 MeV operation. We need a new chiller for those 30 A power supplies required for VISA. Due to the fact that the ATF ran out of funding for FY99, a serious delay is expected in full energy VISA operations.

5). Install Fast detector experiment.

6). Install cameras for VISA matching section

7). Install new waveguide pumping port for the ATF gun waist power load.

8). Install new quadruple YAG laser crystal.

B. Week of October 11 - October 18 (may be extended by a couple of days)

1). Re-Install STELLA experiment.

2). Install VISA undulator at ATF.

3). Test and install new laser oscillator.

2. ATF operations: With many challenges we ran into this week, the ATF staff have done a great job to keep ATF machine and HGHG experiment going. I want thank Jeff and the mechanical group for their help. HGHG continued to make progress this week in observing electron beam energy modulation. We have accomplished this week:

1). Improve the resolution of the electron beam spectrometer at the STELLA experiment.

2). Modify the Pockels Cell for YAG laser system.

3). Improvement the ATF klystron water system.

4). Finish the gun solenoid magnet power supply protection system.

5). Re-align the laser oscillator.

6). Establish CO2 and e-beam synchronization, and electron beam modulation for HGHG experiment for the first time.

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ATF Operations Schedule (Prepared by Xijie Wang)

August: schedules/atf 99-8