2001 ATF Newsletters

Jan | Feb | March | April | May | June - July | Aug | Sept | Oct | Nov - Dec

Hi,

February was an International Month at the ATF, with experimenters from three countries outside the USA running experiments. A group of Russians  from Protvino (in the photo: Vladimir Vogel, Pavel Lunev, Dmitri Valyayev and Nikolai Ukhanov)  were for a run of experiment AE16, Prof. Huang and two of his students (in the picture: YenYin Lin  and Anchung Chiang)  from National Tsinghua University to study laser damage in diamond for experiment AE27 and a large group from Tokyo Metropolitan University and Waseda University (in the photo Shigeru Kashiwagi and Yoshio Kamiya) came for experiment AE22. Some of the results are to be found in this Newsletter.

A major milestone took place in the last week of February: The new picosecond terawatt CO2 laser was used for the first time in the AE22 experiment. The laser power is sub terawatt as yet but we are looking forward to new exciting results to come.Finally, the Visible SASE experiment (AE24) has observed a very large gain. The result is embargoed by the collaboration, waiting for a careful verification and characterization. Stay tuned.

Ilan Ben-Zvi.

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The goal of the run was to understand the effects of the beam charge and longitudinal shape jitter on the resolution of the beam position measurement with RF cavities. Four signals corresponding to the 2.8GHz, 6.46 GHz, 13.6 GHz and 19.4 GHz induced by the electron bunch in the two cavities were measured and analyzed. Figure 1 demonstrates three ratios versus beam charge (Gun phase was scanned to produce charge variation). The signal at the frequency of 2.856 GHz was used as a references, since its amplitude does not depend on the bunch length. One also could see that analysis of high frequencies close to 20 GHz is needed to characterize the ATF beam, with a typical bunch length of the order of a few picoseconds.

Figure 2 represent measurements of the phase detector signal versus beam charge. Linearity of the graph proves that a signal independent of the ATF RF system reference can be produced by a cavity. This is important information towards creating a stand-alone BPM that would be independent of drifts in the Facility RF.Figure 3 demonstrates a good signal-to-noise ratio for an independent reference system at 714MHz for the phase detector.

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We’ve had 5 run days this last block. Heinz-Dieter arrived last Wednesday and stayed through our runs this week.

Last week was dedicated to understanding the beam and beamline optics. A new matching scheme was attempted. Not were just the matching section quads significantly changed, but also all quads before them on the beamline. After the quad settings were inserted, the beam was re-propagated through the entire beamline. The SASE energy now detected is much higher than our previous data (which was  a gain of about 500).  Much more data needs to be taken to accurately quantify the results. In the future, a repeat of this system performance and a further study of the beam optics will be done.

This news reaffirms that the undulator movement effort only a month ago did place it reasonably well into the correct position. A note added by Alex Murokh: We measured the spectrum at 71 MeV and observed a narrow peak at 830 nm, clearly correlated to the SASE signal optimized with the CCD camera.  More detailed information can be found in the attached file.  The data were taken with the PC operated miniature fiber-spectrometer positioned at the beam dump location.

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 Laser Damage Test for a CO2 Laser-driven Linear Accelerator

A CO2 laser-driven linear acceleration experiment is being planned for the ATF. The proposed accelerator structure consists of a lens array arranged in a vacuum. As part of the experimental program, we measured the CO2 laser damage fluence on Germanium, Zinc Selenide, and CVD grown diamond. At a 200 psec laser pulse width, the damage fluence for optically prepared germanium, zinc selenide, and diamond are approximately 0.2J/cm², 0.45J/cm², and 1.2J/cm², respectively. Diamond becomes the material of choice for the proposed CO2 laser-driven accelerator. The ultimate limit of this diamond accelerator at the CO2 laser wavelength is limited by the laser damage field, ~ 200 MeV/m. Based upon the measurement, we will be designing a suitable accelerator structure to conduct a proof-of-principle experiment on structure-based laser driven linear acceleration in a vacuum. We would like to thank ATF staffs for their unreserved assistance.

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A new laser accelerator, LACARA (laser cyclotron autoresonance accelerator), will begin operation in October 2001. This new accelerator will use the 1TW CO2 laser pulse, and will accelerate a bunch of electrons that moves along a 6T solenoid, 2m in length. The solenoid, a "dry" superconducting magnet, is being made by Everson Electric. An energy increase from 50 to 100MeV is predicted. This new device will accelerate an entire bunch of charge, overlapping the laser pulse. It can also be modified to provide a series of bunches about 3fsec in length, spaced by 35fsec, containing about 1pC of charge. These short bunches may be used to study other accelerating structures, such as a dielectric wakefield structure, approximately 10m wide and 1000m tall. The group of researchers is a Yale-Columbia-Omega P collaboration.

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I visited UCLA last Thursday and Friday (February 15-16) and  talked to Ronald Agustsson who are working on the bunch compressor. Here is the status:

1.   One dipole magnet was assembled, and other three components are ready.

They measured the saturation field of the magnet at about 2 KG, I measured the remnant field at about 70 G. Each magnet weighs about 300 Lb. (see picture) I was told that all magnet will be assembled by June.

2.   The vacuum chamber design is finished, machining should start soon.

3.   Work started on the magnet support, and interface with BNL has been requested. I gave them a rail drawing I got from John. A few questions have been transmitted to John Skaritka. All components will be ready in July or August.

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If an event of any significance occurs in the course of your work, there are many ways of dealing with that event, depending on the level importance and impact. At its simplest level, the event is part of your normal day-to-day, skill-of-the-craft work.  You may choose to deal with it yourself and/or discuss it with your supervisor.

Example:  How to Dispose of Glass (NSLS ES&H Highlight #18; Nov. 9, 1999)

For very important events, there is the Occurrence Reporting and Processing System (ORPS). This is a formal reporting system defined by the Department of Energy and is meant to capture events that have serious implications and results.  The event and immediate remedial actions are described and reported to the DOE ORPS database.  A critique is held to examine the event, causes are determined, corrective actions are developed and lessons learned listed.  All of this is tracked in the ORPS database.  Categories of events are defined in theORPS system criteria.  If you witness or are a participant in a serious event, immediately contact your ATF senior management, Bob Casey and/or Nick Gmur.  We will examine and, if necessary, initiate the reporting process.

Example:  Class IIIb laser operated at ATF without documentation, review or approval (ORPS #CH-BH-BNL-NSLS-2000-0003; Oct. 9, 2000).

Some radiological issues that do not rise to the level of Occurrences or where the level of reportability first needs to be determined can be entered via the Radiological Awareness Report system.  The BNL Radiological Control Division manages this system.  Always discuss potential issues with NSLS ES&H personnel to determine reportability. Example:  Worker entered posted Radiation Area without proper protective clothing and without signing or reading associated Radiation Work Permit (RAR #0010-42).

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Last Modified: December 3, 2007
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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 the Research Foundation of State University of New York on behalf of Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit, applied science and technology organization.

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