Accelerator Test Facility

The two runs we had in this period were dedicated to detailed studies of beam effects in electro-optical (E-O) crystals while a new vacuum chamber containing the optical detection system was being prepared for rise time measurements with the streak camera.

The E-O setup is shown in http://www.picosec.bnl.gov/ITEMS/tt0007266.ps where a polarized laser light goes through an E-O crystal (LiNbO3) and then through a quarter wave plate and finally an analyzer. The ATF electron beam is directed through the hole between the LiNbO3 crystal and the ceramic support. The rise time of the E-O signal caused by the electron beam E-field is shown in http://www.picosec.bnl.gov/ITEMS/tt0007261.ps (red). This is to be compared to the rise time of the signal due to a pulsed laser of 10ps width (blue) obtained at the lab using the same photodiode, amplifier and oscilloscope. The E-O signal rise time of 90ps is therefore limited by the detection electronics and particularly the oscilloscope BW. This BW limitation we plan to overcome by using the streak camera in order to take full advantage of the method.

The dependence of the electro-optical signal on the beam charge and the distance between the electron beam and the beam light path in the detector were well measured as shown in http://www.picosec.bnl.gov/ITEMS/tt0007265.ps and http://www.picosec.bnl.gov/ITEMS/tt0007264.ps. The dependence on the beam charge is linear as expected, and the dependence on the distance goes as 1/r again according to theory. The last point comes from the fact that the E-O effect is proportional to the electric field (1/r^2 dependence) times the length of the crystal the laser light travels during the presence of the electron beam pulse duration (r dependence) which is typically 10ps at the ATF.

In addition to the electro-optical modulation of the light beam and the previously observed beam induced opacity, signals with time structure of hundreds of nsec were observed when the crystal intercepted the beam several millimeters from the light path and when the beam struck the ceramic holder. Most signals were the sum of the several effects with the electro-optical component the fastest and the only one that changes sign with reversal of the light polarization or the position of the beam relative to the polarization direction. The very slowly decaying signal may result from ionization of material with an electro-optical effect produced by local charge density resulting from the difference in charge mobility between electrons and ions as the neutral equilibrium is re-established.

The new vacuum chamber was designed and built in order to increase detection sensitivity by increasing significantly the polarization extinction. A large degradation of the extinction was observed when the analysis was done near the control room rather than locally. A remotely controlled analyzer and photodiode are now in the vacuum and under test.

The proofs for our Nuclear Instruments and Methods article on the original detection by this method were returned to the publisher along with the copyright waver forms.

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VISA Experiment(REPORTED BY AARON TREMAINE AND ALEX MUROKH)

Run of June 9th:

Data taken from the last runs indicate little correlation to the proposed correct trajectories sent out by Robert. This could indicate the presence of other uncertainties in the fiducialization numbers. The trajectory data taken also shows a huge kick, 12.5mrad, near the beginning of Section 3. This kick is on the order of a missing dipole magnet. (A steering magnets at full strength gives a kick of ~4.5mrad.) Heinz-Dieter has done simulations showing that the proposed correct trajectory by Robert could not fix this kick. Also, a kick of this magnitude would have to be a gross mis-alignment of the undulator. For results please view the pdf file:

June 9 VISA run

Run of June 13th:

We performed more systematic and accurate studies in the x-direction, and also briefly recorded a couple of y-trajectories. The attached PDF file has all the relevant details:

June 13 VISA run

Run of June 20th:

The important result of this run is that we can straighten the trajectory with the intra-undulator magnets. By using three magnets (before, after and at junction 2-3) we compensated the kick and brought the trajectory down to a few hundred microns walk-off.

As Vitaly suggested, we simulated with MathCad the undulator sections offset and its effect on the trajectory. The best fit to the non-steered trajectories occurs when we assume a sudden offset of about 300-400 microns at the junction of section 2 and 3. Visual observations confirm such a possibility. In addition, the simulated steering scheme to compensate for the offset was implemented during today’s run, and worked fairly well.

Also, for the first time since the shut down we turned on the detector. We measured a steady spontaneous emission of 300 pJ at 400 pC charge.

Run of July 13-17:

We had run days last Thursday, Friday, Sunday, Monday, and Tuesday. Not much noticeable gain was seen, but interesting trajectory measurements were done. Heinz-Dieter from SLAC came out and through his simulations we were able to analyze the trajectories. We horizontally moved the undulator and with the monitoring system were able to move the undulator to <15um of the desired position. At first the peak-peak trajectory was >1.5mm and after several iterations of undulator movement (using Heinz-Dieter’s simulation) it was down to <500um. The agreement between simulation and undulator movement/ trajectory measurement is quite encouraging. This shows we believe that the undulator was not straight for this last set of runs, but we do have the ability to accurately move the undulator in the horizontal plane.

This week the undulator was pulled and moved to the magnetic measurements lab. Robert and his team arrived and with George’s help are setting up the pulsed-wire measurement and will teach Alex and Aaron to re-fiducialize and interferometrically align the undulator sections. If all goes well the fiducialization should be finished the last week in August at which time it will be moved back to the ATF.

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Smith-Purcell Experiment(REPORTED BY HAROLD KIRK)

Summary of Smith-Purcell Experiment Running of June 26-28, 2000:

Principle goals of this running period:

1) Exercise our new data acquisition system. Confirm that software protection prevents stages from traversing beyond limits. Prolific data taking.

2) Operate a BaF2 prism dispersion spectrometer in order to identify the spectrum of the radiation emitted in the forward direction as a result of the e-beam grazing the face of the grating.

Great progress has been realized for goal 1)

Goal 2) will require more work.

Our LABVIEW environment now permits stage manipulations and concurrent data acquisition so that stage scans can be done automatically and quickly. The data is based on the waveform analysis of the ATF Tektronix 644B scope.

Results of this data taking can be reviewed at

http://pubweb.bnl.gov/people/kirk/atf/sp_exp/jun26_00

http://pubweb.bnl.gov/people/kirk/atf/sp_exp/jun27_00

http://pubweb.bnl.gov/people/kirk/atf/sp_exp/jun30_00

Principle results:

I) Our beam profile consisted of

E = 45 MeV, Q = 400 pc, Width = 3 ps, Emittance ~ 1 pi mm-mrad

II) We have determined the cause for previous differences in angular mirror scan profiles. The detector position along the optical collection axis gives different profiles and signal strengths by 1 order of magnitude for 2 cm axial translations. See:

http://pubweb.bnl.gov/people/kirk/atf/sp_exp/jun27_00/2_mscans.ps

III) We have confirmed an angular dependency to the wavelength of the emitted radiation. See:

http://pubweb.bnl.gov/people/kirk/atf/sp_exp/jun27_00/mscan_none_sapphire_I.ps

IV) We see evidence that the longer wavelength radiation has a larger coupling length to the grating. See:

http://pubweb.bnl.gov/people/kirk/atf/sp_exp/jun28_00/pyrex_sapphire_7um.ps

Fitted Gaussian to the xscan distributions yield:

Pyrex-- Sigma = 56 +/- 0.2

Sapphire—Sigma = 56 +/- 0.3

> 7um -- Sigma = 76 +/- 0.8

V) Spectral content for our observed radiation is approximately:

Less than 3 um -- 60%

3 um - 5um -- 20%

> 7 um -- 20%

Our goal for the next run is to implement the BaF2 prism spectrometer and perform a spectrum analysis of the detected radiation.

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Technical Operations (REPORTED BY BILL CAHILL)

June 23:

Over the past two weeks we have been able to move our people into the new offices of 820-M. We now have all of the ATF staff under one roof. Mechanical assistance was offered to HGHG on the realignment of the three camera’s that were moved to access the new liquid crystal CO2 beam display. I believe this saved a lot of time and frustration. All three camera’s were being powered by a single power supply, loading down the system, Marc has ordered additional supplies and will install them as soon as they arrive. We also provided electrical help with the HGHG pneumatics for the pop-in monitors and video switching system. The remaining two UPS supplies were installed in the MCR to protect the CAMAC control system and the repair of various Darlington transistor power supply channels were needed for the continuation of operations. Last week the workload consisted of installing the main discharge chamber at the Terawatt pre-ionizer along with an alignment that sets the gap on the electrode screen. Clamping rings were installed and torqued to hold the pre-ionizer in place and the connection was made up to allow for vacuum testing. Unfortunately, the vacuum control interlock network is not finalized and we cannot continue with the system check-out. Scott Buda will be back from vacation on Wednesday and hopefully we can complete the interlock chain and resume testing. The new hardware has arrived to replace the Russian stock and is being installed. In addition to all this activity, the technical staff of the ATF continues to support the control room operations on a daily basis.

June 30:

The majority of the week was spent assisting the HGHG experiment with the ordering, design and construction of tv monitor power supplies and power distribution for the lamps used in the experiment. Assistance was also given in the trouble-shooting of the failed power supplies for the trim magnets within the undulator. Luckily, these supplies are not needed at this time but will have to be repaired as soon as possible for future experimentation. We attempted to install a replacement power supply for the focusing into the undulator but were unable to attain the manual from NSLS to wire it in properly. Hopefully, we can find the information needed to make the changeover as our loaned supply is needed badly for another function. Time was spend inventorying possible PCB equipment. A test for high levels remain on the old high voltage transformer inside the gun modulator, after which, we are PCB free. The Failed UPS power system in the control Room was replaced and at this time, all CAMAC crates are now protected. The mechanical team has achieved high vacuum on the terawatt pre-ionizer at a pressure of 5x10-5 and the vacuum control system appears to be working properly. Before closing the main pressure vessel, we will leak-check all components. Aside from all these responsibilities, the technical staff of the ATF continues to support the control room and experimental operations on a daily basis.

July 21:

The high voltage Maxwell pulse generator was sent out for repair and has arrived in time for installation for the HGHG run next week. Don Davis and Bob Harrington have been installing the gas lines for the main discharge cell of the terawatt laser and securing the parts needed for the exhaust line for the pre-ionizer. The heater assembly for the YAG amplifier has been installed and the bracket for the active mirror relating to the YAG oscillator has been machined. Electrically, Marc replaced a bad triode in the third stage on the linac 1 kw driver. The unit has been retuned and is running to ATF specifications. The CO2 pulser has been electrically tested and installed back in the CO2 room. The high voltage contactor needed for the gigawatt has been built and is in the process on installation.

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ATF Engineering Meeting (REPORTED BY XIJIE WANG)

June 9:

1. ATF facility improvement project for next couple months: I propose three areas for ATF facility improvements over the next couple month :
A. TW CO2 laser: The review and testing for discharge cell is almost complete, Igor should follow through the final report. The goal is to get CO2 laser pulse less than 50 ps(FWHM) and energy more than 3 J by the end of this year.
B. YAG laser and beam improvements: We need significant improvement in laser profile, pointing stability and imaging in next couple month. July beam studies time will be devoted to the beam improvements. Marcus needs to follow through the crystal polishing. We should also be planning to move quads in the tunnel to improve the steering.
C. Stability and reliability studies: I am now investigating next round ATF stability and reliability projects. I believe that, the good experiment results we had in the last year largely due to the time and effort we spent on the stability and reliability improvements. I suggest we finish on-going projects, and next round will be more RF and beam diagnostics.
2. Next week ATF jobs:
A. Scot install key pad.
B. Bob work with Marcus on Monday for YAG laser transport tube, and work on the CO2 laser after.
C. Mark will first finish the cables for Marcus, and install dipole magnet shunt for current measurement. Continue work on the linac water system.
3. Fast detector experiment: they are in the process of testing new chamber, they need to talk to Bill for safety, and must have vacuum in the new chamber better than 5x10^-8 for next round experiment.

June 16

ATF schedule: VISA has canceled scheduled alignment next Monday. HGHG will user Monday to install new diagnostics and beam alignment. Due to the problem with the YAG laser Pockels cell for CO2 synchronization, more scheduled modification may need until I can get in touch with STELLA people.
YAG Laser: Marcus reported Pockels cell failure today, he has sent out damaged unit out for repairmen. This unit has failed twice last year, maybe we need a back up unit for it. Marcus has not get any definite answer on the crystal polishing.
Next Monday ATF maintenance jobs: Install key pad for the experimental hall, connect control room UPS units (Mark and Malone), Harrington will continue work on the YAG laser job on Monday, and CO2 afterwards.
CO2 job: there was much confusion this week on CO2 jobs. I request a meeting Next Monday 10:00 AM. The people I would like to be present are Igor, Ilan, Cahill, John, Harrington.

June 23

ATF schedule modification: July 5 beam studies time will be changed to Maintenance day since next week no maintains day. We also make July 24 and 31 maintenance day split for HGHG (which starts 3:00PM). We are considering more run days for HGHG in weekend, so please keep everything open, do not schedule any work at weekend may conflict with HGHG run.
Martin introduced a new engineer Mr. Hu.
Next week HGHG jobs: install camera power supply, make ID2 independent of ID1, and install new GW CO2 power supply.
Martin will look into the possibility of helping out on better support for VISA steering magnets (three locations) and install N2 bleed up line for the experimental hall.
TW CO2: all jobs on TW CO2 go through Igor, please contact Igor if you have good suggestions for TW CO2.
Fast Detector Group request survey help, they need pre-survey the installation. Contact John with account number.
July 7 visit by The S&T Steering Committee, I am in charge of the tour. Keep your area clean: CO2: Igor. experimental Hall: Cahill. FEL diagnostics room: Marcus. control room: Malone. Gun area: Vitaly.

Have a nice holiday.

July 7:

ATF schedule: due to the failure of CO2 pulser, we go back to the old schedule. Monday maintenance day, and Wednesday beam studies starts at 11:00 am.
ATF critical parts list: I asked Marcus and Mark to prepare a list for the critical parts may take more than 10 day to repair or purchase.
Shield support for the beam line 1: End of the beam line 1 shield need better support, this will be done first thing next Monday.
Mark first fix the YAG amplifier heater, then HGHG second dipole small trim power supply.

5. Solid state modulator: I was impressed by the progress of the solid state modulator technologies, now MIT and NLC are adopting this technology, I suggest we should also consider this for our energy upgrade.

July 14:

1. ATF schedule: Next week ATF maintenance day is on Wednesday, and Friday beam studies time experimental hall will open for access.

2. GW CO2: Igor has shipped the pulser to Maxwell last Friday, Bill and Mark are now following the status. We were told the unit will be fixed and ship back to BNL next Tuesday after the test if they get paid.

3. Wednesday jobs: Mark will check the RF system, including 1 KW and modulator. Bob will help to install the heater for the YAG laser.

4. YAG laser: next week’s Friday beam studies will be used for cathode cleaning and crystal testing.

5. VISA: Visa is planning to remove the magnet for testing, Sam agreed to provide one day help from vacuum group and Mike. Don will also help on that day.

6. TW CO2: Bob and Don will work on the TW CO2 except next Wednesday.

7. Fast detector: new equipment installed and surveyed, I told them they must have better than 5x10^-8 vacuum for operation.

July 21:

ATF schedule: Significant modification on ATF schedule was made, all VISA running date now given to HGHG, and plus one beam studies date next Friday. Please look up at ATF we site for new schedule.
ATF maintenance next Monday: Marcus will make sure the YAG laser alignment is good; Harrington will fill up the nitrogen tank and water for the magnet, gun and linac water system. Cahill check all AC systems. Marc finishes any remaining checks on the RF system and magnet power supply. Malone will do computer back up. Computer will not available during the back next Monday.
ATF August and September shutdown: ATF need a long shutdown to up-date the system and improve the performance, presently we are considering three weeks shutdown in the last August and early September, here is the initial list we are considering:

Install and test new oscillator.
Install new front end optics.
Fix the contact problem of the beam shutter.
Both radiation and laser interlock check.
Test new crate controller.
Install new water system for the linac.
Fix the high energy slit
Alignment of the quadrupole magnets.
New air cleaner filter.

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