2000 ATF Newsletters

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December 28

Greetings everybody,

We grieve the unexpected death of Professor John Walsh of Dartmouth College on December 5th. John was one of the first users of the ATF, a leader in the FEL community, winner of the FEL Prize, the spokesperson of the Smith-Purcell experiment on the ATF and a wonderful person. Our condolences to his family and friends.

This is the last report of the year 2000. It is also the 49th report since I started this series. I would like to thank all the contributors for the Newsletter, ATF staff and users.

A graduation ceremony took place at the University in Stony Brook on December 17. I had the pleasure to hood  Dr. Adnan Doyuran, who has done his thesis on the High-Gain Harmonic Generation experiment. Of course thanks go to the funding of ONR and to many people, including  Li-Hua Yu who played a major role in Adnan's thesis research, Marcus Babzien and Igor Pogorelsky who taught him laser optics, Xijie Wang and Vitaly Yakimenko on the accelerator, Bob Malone on the software and of course the dedication of the technical staff Bill Cahill, Bob Harrington and Mark Montemagno.

Adnan's Ph.D. dissertation can be found on the web at 

Adnan

Since 1992 the following 15 graduate students obtained a degree based on research carried out at the ATF:

Xijie Wang (Ph.D. 1992, Univ. of Calif. at Los Angeles)

David P. Russell (Ph.D. 1992, Princeton University)

Marcus Babzien (M.S.I. 1993, University at Stony Brook)

Alex Grey (M.S.I. 1993, University at Stony Brook)

Karl Kusche (M.S.I. 1993, University at Stony Brook)

Jim Blastos (M.Sc. 1994, Massachusetts Institute of Technology)

Richard E. Stoner (Ph.D. 1994, Massachusetts Institute of Technology)

Ken Woods (Ph.D. 1995, Dartmouth College)

Joe X. Qiu (Ph.D. 1997, University at Stony Brook)

Yabo Liu (Ph.D. 1997, University of California at Los Angeles)

Jim Fang (Ph.D. 1997, Columbia University)

Denis Palmer (Ph.D. 1997, Stanford University)

William Klein (Ph.D. 1997, University of New Mexico)

Palmyra Catravas (Ph.D. 1998, Massachusetts Institute of Technology)

Adnan Doyuran (Ph.D. 2000, University at Stony Brook)

Finally, the ATF web site moved to a new server. If you marked ATF pages as "Favorites" please mark them again. The web URLs given above are updated.

Have a Happy New Year,

Ilan Ben Zvi.

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This is a brief report about the MINOS ion chamber test run on November 20-21, 2000.

Our group consists of Brookhaven National Laboratory physics department, Fermi National Laboratory, University of Pittsburgh, and University of Wisconsin. We expect physicists from Northwestern University to participate in future tests.

The goal of the experiment is to learn how ionization in gases saturates at high charged particle intensities. There are many competing factors when measuring this ionization. They can be classified according to their origin as either intrinsic to the processes in the gas or artifacts of the apparatus geometry and electronics. To disentangle the two effects we must understand the electronics and noise level in detail as well as measure the total charge of the incident beam with good accuracy.  

The test run on Nov 20-21 was successful in many respects. In broad terms, we learned how the ATF accelerator operates, we cleared many hurdles in setting up the apparatus, we created the proper trigger conditions for our data acquisition electronics, and we took several hours of useful data. The total charge of the beam was measured in a Faraday cup behind the ionization chamber. We were able to run the accelerator with a total charge as low as 7 pC with about 10% noise. We were also able to run at 800 pC in multi-pulse mode. In multi-pulse mode we could measure the effect of saturation as a function of time.  This data is being analyzed, and we should have preliminary results soon.

In the next run we would like to make much more detailed measurements with small changes to the apparatus.  Mainly we would like to push the dynamic range both lower and higher.  We would like to replace the cable to the Faraday cup with a triaxial cable of lower noise to reach 1-2 pC measurement capability.  We would also like to control the beam spot size  much better by placing a flag in front of the ionization chamber.  

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After the shutdown was completed, we started running the VISA system again. Similar to last time, trajectory studies in the horizontal and vertical were measured. Also similar to last time we are still seeing orbit kicks, the largest still at the junction between Sections 2 & 3.

The undulator was monitored and did not move (<20um) during the pumpdown procedure to the accuracy of our monitoring. The new horizontal sliders seem to be doing their job.

After many radical ideas about the source of this kick, a pragmatic independent check of the alignment process was done. An inconsistency seems to have turned up in transferring the undulator fiducials to the ATF experimental hall from the magnetic measurements laboratory.  A predicted misalignment was obtained from this study and put in a trajectory simulator. The predicted trajectory was compared with the data taken above for the horizontal  orbits and a reasonable agreement was found.

If this is the case, then our near term goal is to slowly move the undulator back into place while independently checking the trajectories with a beam based alignment algorithm. This process should converge to moving the undulator  to within the original alignment tolerances. Remember, now we have the ability to move the undulator vertically as well as horizontally so any misalignments can hopefully be corrected (as long as the range of motion on the adjusters is large enough). Also, the alignment monitoring system can distinguish undulator moves to <15um.

The reason for the kick to be largest in Section 3 is for the following. When the magnetic measurement data is compared with CMM data taken on the undulator frame, a distance between the magnetic center and the mechanical center can be found. For Section 3, the distance between these two axis is the largest. Any systematic error in the alignment process in the ATF will show the greatest error when the trajectory studies are done at this point.

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We successfully sent an electron beam through the Compton cell and miniature permanent-magnet quadrupoles on beam-line 1. The purpose of these quadrupoles is to allow us to generate a very small spot size. The initial results are encouraging. We did not have time to optimize the tuning but we did observe a 40 mirons (sigma) electron beam in the middle of the chamber for 0.5 nC beam. The beam was refocused on the spectrometer screen after Compton cell. The steering due to orbit error was not minimized but it did not suggest any problems with the miniature quadrupoles. There is reasonable confidence in the further reduction of the beam size by factor 2-4 due to smaller charge (nominal charge expected to be around 100 pC) and a better tune. This  part of the experiment is expected to continue in the second half of the January. 

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The MathCAD interface to our control system was extensively used for everyday operations this year. 

One example can be a program that automatically collects information about the photo-injector and laser performance every morning. That one page program has proven to be very useful in the operator independent basic parameters recording. A sample of pages generated by the program can be found at

Photoinjector  

The data is used to evaluate changes in the laser stability, reasons for quantum efficiency drops, etc. 

Another example are gun and linac feedback systems, usually used to overcome temporally problems with RF stability. These problems were resolved by fixing the sources of such instabilities (replacing unstable power supplies, fixing bad contact or soldering joint). Since it takes weeks to find intermittent problems, the feedback programs allow us to minimize the effects of such a condition on the experimental program. We often use the linac feedback program now but did not use gun feedback since late October but it is ready to go should we need it. 

Another example of a successful use of the MathCAD package is the linac feedback program. There were problems with the implementation of a linac power feedback system. The error signal, derived from the charge measured on the High-Energy Slit (HES), depends on many beam parameters as well the value of the HES opening (it varies from one experiment to another). The program written in MathCAD allows the operator to change the feedback loop parameters on the fly and thus obtain a stable feedback.

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The ATF terawatt CO2 laser is not in service yet. However, a festive moment expected by the ATF users is approaching. An intense work is in progress with a near-term goal of bringing the high-pressure booster amplifier on line at sub-terawatt output peak power (~10 J @ 30 ps) in January 2001. This will be ~300 time increase to compare with the presently operated at the ATF laser that still enabled our users to achieve break-through scientific results (e.g., record x-ray yield in Thomson scattering, monoenergetic staged laser acceleration, the first high-gain harmonic generation from wigglers...).
Our next schedule is to use 300 GW laser beam to demonstrate greatly enhanced x-ray yields and nonlinear effects in the Japan-US collaborative Thomson scattering experiment (February 2001).
Later in the year there will be: STELLA II, vacuum acceleration, LACARA (laser acceleration in superconducting solenoid) and other user's experiments.
Simultaneously, we will continue CO2 laser improvement to ~30J @ 10 ps. Our longer-term goal is ~10 J @ 1 ps that is an attractive regime for LWFA as well. However, this requires an upgrade of the present 10 ps Nd:YAG laser, which is used at the ATF to slice picosecond CO2 pulses.
In production is a capillary discharge assembly for channeling the CO2 laser beam. This device can be placed in the ATF beamline #1 in the middle of 2001 to study new approaches to high-efficiency x-ray generation and electron acceleration.
Thus, we have high expectations for the upgrade of the ATF's CO2 laser in 2001.

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A number of safety violations involving compressed gas and liquid storage drums in the CO2 areas were noticed and corrected. 

1. The green drums that were used to temporarily store the transformer oil from the Marx generator were not labeled as such. 
2. The plastic drums that are in the terawatt room needed labels. 
All containers that have a liquid in them must have a proper label. A proper label is the ones with the four color hazard diamond. They are a stock item in the light source.      
3. There were two compressed gas bottles, on carts, on the south end of the Marx generator. 
Carts are to be used to transport compressed gas bottles, not permanent storage. If the bottles are to remain in there present location then they should be secured properly. 
4. There was a compressed gas bottle of nitrogen in the FEL room. It was on a cart and was missing a cap. 
 
Everyone who needs to handle compressed gases MUST have compressed gas training BEFORE the do so. 
If you have any question please contact me.

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Editors: Andrew Ackerman & Nicholas Gmür No. 22 Date: December 11, 2000

ESH Review of Experiments at the NSLS, ATF, and SDL

Experimental Review Goals
All experiments conducted within the NSLS Complex (NSLS, ATF, SDL) must be reviewed for Environment, Safety, and Health (ESH) concerns. The goal of these experimental reviews is to minimize risks through involvement with the ESH Staff. Any engineering or administrative controls established by the review to protect personnel, equipment and the environment from harm must be adhered to.

Recent Incident
Recently, an event involving work with laser systems at the ATF illustrated a need to assure that our Users remain aware of this review requirement. A change in a user's equipment on an ATF beam line introduced new risks that were not captured in the review process and not adequately controlled. Fortunately, the ATF staff was alert to the activities in the experimental hall and was quick to take action. There was no injury or environmental impact, but it was clear that planning and review for this experiment was inadequate.

The Review Process
Policy for ESH review of experiments is on the web as NSLS PRM 1.3.5a: Experiment Safety Review. We meet the requirements of that policy through use of our Safety Approval Form. Experimenters are expected to report the materials and equipment necessary for their work, provide a complete description of the tasks involved, and identify any risks presented. For routine, low risk experiments, we ask that the forms be completed one week in advance of the experiment to allow time for our review. For work that presents significant risk (hazardous gasses or chemicals, biohazards, radiological materials, human or animal materials, or work at high pressure or with lasers) we expect lead-times of a month or longer to allow for discussion, review, and agreement on appropriate controls. We expect experiments to change and realize that changes cannot always be anticipated. You must tell us when that happens and we will work with you to keep things moving while still assuring attention to any ESH concerns.

Assistance - For Your and For Us
New Users are coming all the time. Please help us assure that they know what is expected for review of their experiments. Andrew Ackerman (x5431) is the primary contact for this program, but any member of the NSLS ES&H Staff can help with questions. Help us by providing timely and complete information about your experiment. In almost 20 years of operation, we have never had a serious injury resulting from our experimental program, our Users have always been forthcoming with details about their work, and we have found a way to accommodate almost every proposal received. Please help us maintain that record for the next 20 years.

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

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE’s Office of Science by Brookhaven Science Associates, a limited-liability company founded by Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

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