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Site Details ATF Newsletters 
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1999 ATF NewslettersMarch | April | May | June | July | August | Sept | Oct | Nov | DecMarch 12 | March 19 | March 26
All, This is the first of the new weekly report on the status of the Accelerator Test Facility. Information on the ATF and its experiments can also be found at the ATF Web Site. Best regards, Ilan Ben-Zvi. Special notice: Monday, March 15 through Tuesday March 16 there is a Laser Panel Meeting in Room A of the NSLS. The details are in the appendix below.
All mirrors in the radiator were changed to the improved design. Two of the new mirrors do not meet the specifications and must be replaced. New modulator chamber is installed with pop-in diagnostic. Gap control is complete but some interface bug must be fixed. CTR micro-bunching diagnostic installed. Air and electrical controls have to be installed. Electricians pulled video and control cables for new pop-ins on HGHG equipment. Vacuum group leak checked Beam line #2 and turbo station. The beam line was pumped down. In the last week we had four days of STELLA (Staged Electron Laser Accelerator) experiment run. Goal of the run: reestablish and demonstrate electron micro-bunching effect downstream of the IFEL (inverse FEL) wiggler using CTR (coherent transition radiation) diagnostics. Up to 1 GW CO2 laser pulses have been used to impose periodical energy modulation on electrons propagating inside the wiggler. Using a photo-detector (sensitive within a spectral region of 1-5.5 micrometers), we measured a strong signal when electrons were synchronized with the laser pulse in the wiggler. Improvements in the electron beam focusing and diagnostics let to an increase of the signal 10 times to compared with previous results published in PRL. Quantitative characterization of micro-bunches will be attempted in future runs after doing further improvements in the optical diagnostics and stability of the electron beam.
Installation of US-Japan collaboration Compton scattering experiment started in the ATF beamline #1. The IFEL wiggler has been removed in order to provide a clear path for the beam to the Compton cell. The electron beam was transported through the line to the spectrometer and the bremsstrahlung background was reduced by two orders of magnitude. Some broadening of the electron spectrum was observed and will be studied. The STELLA spectrometer has been safely relocated east of beam line 1, the Compton cell has been assembled with optics and installed onto the rail system of the STELLA ICA table. The transport line to the beam dump has been installed and is waiting for the final diagnostic installation. This week we received the report of the analysis of the two BPM runs made this year by the BINP-Protvino group headed by Vladimir Balakin. The results show a measured resolution of 0.19 microns for a single 0.5 nC bunch. The report mentioned that the BPM show promise of sub 0.1 micron single shot resolution (!). Undulator Sections #2 and #3 were individually set up on the pulsed wire bench in the normal (upright) orientation for tuning. X and Y trajectory straightness of approximately ½ wiggle amplitude peak-to-peak was achieved. This is a factor of two better than required. Section #1, which had been tuned last month, was shipped back to SLAC for replacement of the missing fiducial and for recalibration on SLAC’s high-precision CMM. Two weeks ago the HP straightness interferometer electronics developed an intermittent malfunction. The display unit began locking up after warm-up. Hewlett-Packard was contacted and this week the unit was shipped to HP for repair. Turnaround time is expected to be 2-3 weeks. Since Robert Ruland has taken the wire finders back to SLAC for modifications to improve their stability, we cannot make interferometer measurements anyway, so this turns out to be a convenient time to make repairs. In the meantime, we are borrowing an identical display unit from Frank Karl of the AGS Survey Group. The idea of modeling the trajectory of a 72 MeV e-beam in the undulator with the pulsed wire was considered and discussed at length among members of the collaboration. It turns out that the current pulse in the wire would have to be inreased from less than 2 amps to about 40 amps, at a voltage of 2 kV and pulse length of 10 milliseconds. This is not trivial and no such pulse generator is available off-the-shelf. This idea is on the back burner for now, since it is not essential to our understanding of the trajectory straightening operation. Next week we plan to set up Section #4 together with #3. We will tune up #4 and also check the trajectory through the joint between them. We will also check the match of the downstream termination section to the downstream end of Section #4. Still to be done are remeasurement of Section #1 when it returns from SLAC, a recheck of each section in the 90-degree orientation (to eliminate the effect of wire sag) and checking the trajectory through the joints between Sections #1 and #2, and between #2 and #3. By this time we hope to have the wire finders back and we expect Robert Ruland to return to do the interferomery measurements. Last week Roger Carr and Ben Poling of SLAC completed a 2-week stay at BNL. They assembled the VISA vacuum chamber and did a leak check. The Mechanical Group and Vacuum Group provided generous amounts of assistance.
Bill Cahill reports: 30 amp Darlington power supply has been finished.
gun hutch joulemeter: 4.3% sigma, 28% p-p gun hutch photodiode readout: 2.2% sigma, 13% p-p both recorded over same 500 shots, and both larger than UV joulemeter in YAG room, which gave 1.8% sigma, 10% p-p
The acceptance test of the Terawatt CO2 laser amplifier built by OPTOEL Co. (Russia) has been completed this week. An optical gain coefficient of up to 2%/cm at 7 atm gas pressure has been demonstrated. With this measurement we have completed the terawatt amplifier contract. Next on our program: Generation of 10 picosecond pulses from the preamplifier, to be directed later on into the terawatt amplifier for full output. The cathode of the gun was laser-cleaned. The quantum efficiency improved at least a factor of 4 to 0.1%. The QE fluctuation is now less than 10%(p-p) over 1mm radius. Detailed measurement of the QE on the suspect spot shows no sign of anomaly. Double electron beam still present. No bellows were installed on the gun exit window due to suspect coloration of the bellows. A new Mg cathode is under preparation, it will be back at BNL by the end of next week. For the week of March 15, 1999, the ATF Schedule is: Monday, March 15, 1999 8:30 AM - 4:30PM: ATF Maintenance. Experiment hall open for HGHG profile monitor alignment and Compton installation. Tuesday, March 16, 1999 10:00 AM - 5:00PM HGHG experiment, physicist: YU, Operator: Cahill Wednesday, March 17, 1999 9:00 AM - 5:00 PM Compton Experiment, Physicist Pogorelsky, Operator Montemagno Thursday, March 18, 1999 9:00 AM - 5:00 PM Wakefield Experiment, Physicist Wang, Operator Harrington Friday, March 19, 1999 9:00 AM - 5:00 PM Compton Experiment, Physicist Pogorelsky, Operator Montemagno The date for the meeting is March 15 -16, 1999 at Brookhaven National Laboratory, National Synchrotron Light Source, Seminar Room A. The meeting will consist of: 1. Presentation of the ATF photocathode system 2. Visit to the ATF 3. Informal discussions centered about the three issues: a. The short term question: What improvements can be made to the ATF’s Nd:YAG laser in a period of weeks, to the current laser. b. The medium term question: What improvements to performance or reliability can and should be done on the current laser on a scale of weeks to a year. c. The long term question: What laser technology is available to make a new, better laser, their risks and potential on a scale of two to three years. The long term question is concerned with what is the best solution to the particular laser needs for photocathode RF guns. These needs include strict amplitude and phase lock stability requirements, good pointing stability, good mode and high mode stability, output pulse length in the few picoseconds range with an arbitrarily shaped temporal profile. The energy needed in a single pulse is 5 to 10 mJ at a repetition rate of about 100 Hz. The agenda is tentative and can be changed at any time to allow flexibility. Monday, March 15
Tuesday, March 16
Participants in the meeting: Laser panel - has the charge of writing an independent recommendation for future directions.
In addition, BNL participants in the meeting will be:
Laser industry participants:
Last Modified: December 3, 2007 |
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