Accelerator Test Facility

A new experiments has been approved for the ATF by CAP Head Bob Palmer. This is the "Structure-based Laser Driven Acceleration in a Vacuum", AE27. Spokesperson: Y. C. Huang, National Tsinghua Univ., Taiwan. The experiment will start soon. The number of approved experiments is now at 15.

I have approved a feasibility test for a new potential ATF experiment: MINOS Detector Experiment, whose spokesperson is Milind Diwan, of BNL's Physics Department. (See item below).

The HGHG Experiment is reporting new results, and VISA has undergone a large shutdown to improve the stability of the undulator. The shutdown was very successful and the undulator seems now well aligned.

The YAG laser has a new oscillator (congratulations!) and the laser performance (after some usual teething problems) is now improved in a few performance measures.

Finally, we are making the user's life more comfortable. With the move of ATF staff to the new 820M building and some other rearrangements we have cleared two laboratory areas for user set-up of equipment and for storage. At the same time, the set-up area (which was too small and cluttered) in the northern side of the Control Room is being converted to dedicated control area for user's experiments. I would like to thank Karl Kusche for his efforts on behalf of all users.

Ilan Ben-Zvi.

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HGHG Experiment (REPORTED BY LI-HUA YU)

During the past runs, our HGHG study achieved major success in 4 different subjects:

1. Adnan and Marcus’s autocorrelator pulse length measurement has obtained a stable and clear result. The following is one of the result for 8ps e-beam pulse case, the 9.9ps autocorrelation FWHM should be divided by 1.5 to obtain the pulse length of 6.6ps FWHM. For a 6ps e-beam the result radiation by this method is 5.7 ps.

8_25_HGHG_autocorrelation.jpg

2. We steered the e-beam to monitor the output by a pyroviewer. The radiation pattern is moved by 2.5mm in the horizontal steering without blurring the pattern. This may be useful in future cascading of HGHG stages, when the output of one stage can be steered for alignment as the input of the next stage.

8_25_HGHG_steering.jpg

3. The 2^nd, and 3^rd harmonics at 2.6 and 1.7 micron of the HGHG output at 5.3 micron have been measured, showing agreement with simulation and analytical theory within the error bar of the measurement.

The 2.6 micron power is found to be

1.5*10^(-4) of the fundamental at 5.3 micron, as compared with 6*10^(-4) based on simulation provided by Sandra, and also as compared with Juhao Wu’s analytical calculation result of 3*10^(-4).

The 1.7 micron power is found to be

7*10^(-3) of the fundamental at 5.3 micron, as compared with 10^(-2) based on simulation provided by Sandra .

The measurement of the harmonics vs. e-beam energy modulation generated by HGHG showed linear dependence for the fundamental at 5.3 micron confirming energy conservation. while the 2^nd and 3^rd harmonics showed exponential increase for larger modulation, indicating highly non-linearity and saturation.

4. Timur’s Michelson interferometer measurement generated very clear interference pattern. For 6ps e-beam, the pulse coherence length based on this method is found to be 5.5 ps, agrees with the autocorrelator measurement. This showed that the pulse is fully coherent, a very important result.

The interference fringes is in

8_25_HGHG_interf.bmp

The fringe visibility as a function of delay is in

8_25_HGHG_autocorrelation.jpg

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MINOS Detector Feasibility Test (REPORTED BY MILIND DIWAN)

We will be testing ionization chambers at the ATF for the MINOS experiment at FERMILAB.
MINOS stands for "Main Injector Neutrino Oscillation Experiment". Fermilab has a new accelerator that can produce very intense proton beams of 120 GeV. These protons can be used for making intense neutrino beams. The protons come in 10 micro-sec long pulses every 2 sec; they are focused onto a graphite target. The positively charged pions produced in the reactions of protons on carbon are focused by magnetic lenses called horns into a parallel beam with a width of about 50 cm. This beam of pions is sent through a 700 meter long evacuated decay tunnel. Each positive pion decays into a muon type neutrino and an anti-muon in flight. The resulting beam of neutrinos is sent to a detector located 732 km away. The goal of the experiment is to see if the muon type neutrinos convert (or oscillate) into other types of neutrinos over that distance. There are strong indications that this will happen from studies of neutrinos produced in the atmosphere by cosmic rays. This physics is of fundamental interest because it would indicate that neutrinos have mass as well as violate the principle of separate lepton number conservation.
It is very important for the final result of the experiment that we understand the intensity of the neutrino beam. This is done in two ways: by measuring neutrino interactions in a detector located very near the end of the decay tunnel and by measuring the intense flux of pions and muons in the decay tunnel. Although the former is the more important measurement, the second measurement has to be carried out to get additional crucial information. The second measurement has several conditions: 1) we must detect any shift in intensity over the running time, 2) we must detect any shift in the direction of the beam, 3) the detector response must be linear over a wide dynamic range (10**5 to 10**10 particles per square cm per 10 micro-sec). The simplest devices that can measure such intense beams are ionization chambers. Although these are old devices, it appears that there is limited amount of information on their stability and linearity. The two references that we have used (S. Palestini, et al., NIM A421 (1999), page 75 and J.W. Boag, et al., British Journal of Applied Physics, 222 (1952)) don't produce consistent answers for our geometry. Therefore, we have decided to make measurements and gain experience ourselves. The ATF appears to be the ideal source for such a test. The intensities and beam size are appropriate. The time structure could be expanded to 1 micro-sec. But most importantly, the intensity can be measured by other devices such as a Faraday cup for good calibration. We will carry out a preliminary test in late November in beam line #3. We hope to carry out a series of tests eventually with our final design. In the process we hope to learn more about the non-linear processes in various gases under different conditions.
Collaborators from FERMILAB, University of Pittsburgh, North-Western University, Wisconsin University, University of Athens, and BNL will participate in this test.

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VISA Shutdown (REPORTED BY ALEX MUROKH)

The big VISA shutdown has been completed and we are working our way towards a run.

· beam matching section was reinforced with stronger quadrupole
· the new support stages for undulator magnets are installed
· vacuum - coupled vertical adjusters are installed
· BPMs were equipped with bigger periscope mirrors and installed
· undulator magnets alignment is completed
· both Red and IR alignment lasers are aligned with the undulator axis
· BPM # 9.5 in the matching section WAS installed
· the system will be prepared for the pumpdown by the day end
· magnet sections position monitoring cameras need to be installed before starting to pump
· pumpdown done
· we made new covers to protect adjusters
· "mini" steering magnets for undulator matching section are being fabricated in UCLA

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YAG Laser Improvements (REPORTED BY MARCUS BABZIEN)

Work on the YAG system over the past few weeks has been primarily to improve amplitude stability on the cathode. The improved version of the oscillator has been installed, but initially the changes in the system led to a deterioration in performance. Typical operation for the system was shot to shot UV energy jitter of 2.0-2.4 % sigma. The increased jitter occurred because of a drop in energy of about 10% in a fraction of the pulses, with the remaining pulses in the normal energy range. This signature has made it possible to correlate the behavior reliably to the gain delivered in the preamplifier. Initially, the new oscillator, installed shortly before the behavior was noticed, was was suspected as the source. However, RF spectra of the oscillator pulse train are very clean, and the seed pulses exiting the amplifiers have a jitter of 0.3-0.5% in the absence of gain. After much work the problems have been fixed. The laser statistics are now much improved (see:

YAG_stats.htm )

The amplitude jitter returned nearly to its old, stable value (more work needs to be done), and the phase stability is very good. There is a remarkable improvement in the pointing stability, which now stands at 0.2% horizontal, 0.1% vertical! With the new 4th harmonic crystal the uniformity improved from 12 (17) to 10 (9) percent in the horizontal (vertical).

In addition, maintenance and upgrade work was done on the replacement of gun hutch optical hardware, vacuum transport line components, fourth harmonic crystal replacement, water chiller replacement, and high voltage pulser replacement.

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User Facilities and Control (REPORTED BY KARL KUSCHE)

New Users Set-up Area:

With the retirement of Bill Cahill and imminent relocation of the technician's room, ATF users will now have two laboratory spaces in bldg. 820 dedicated for experiment set up and limited equipment storage.

Computer Access in the Experiment Hall:

Two 486 notebooks were recently picked up from the BNL excess list, and are configured to run eXceed to allow for access to the ATF VAX X-windows system in the Experimental Hall. The first notebook is now in place at the head of beamline #2. Anyone with access to the ATF "operator" account (or one of the valid user accounts) can log into this PC to call up control windows for the linac, pop-ins, etc.
Please keep the following in mind:
1) Due to the small screen size, eXceed has been configured to "pan" the active window as the cursor hits any side of the screen. Also, be patient with program loading - the 486-50Mhz is doing its best!
2) As with the Control Room terminals, please remember to LOG OUT when your session is finished at the end of the day or run. You don't have to power the notebook down, but please leave the Windows 95 login window visible for the next person.
3) Keep the notebook plugged into the wall charger at all times. The batteries are able to keep the system alive only long enough to survive short power outages.
4) Contact Karl or Marcus for assistance - don't try to troubleshoot the system yourself. In fact, you may want to ask us for a demo prior to your running time so that any bugs can be taken care of ahead of time.

New ATF Computer Room:

ATFSERVER1 and its printers are now fully set up in the new location, bldg. 820M (rear office area) room 14. The same 24/7 availability, software, and file access apply as before. The security lock on the door has the same combination and keying as well. If you are interested in using any of the old software titles on the shelves, please ask Karl or Marcus.
Printers: Two printers are available for printing in the 820M office area. The PaintJet XL300 is available as before, and the new HP 3150 Multifunction printer is shared on the server for black/white laser jet printing. The new HP Color LaserJet 4500N is located in the ATF Control Room, but is shared via the network on ATFSERVER1. See Karl or Marcus if you need help connecting. CAUTION: Each printer requires different transparency paper - if the wrong type is used, the printer will be damaged!
FAX: New HP 3150 Multifunction also serves as a plain-paper FAX machine, located in 820M room 14, same FAX number as before (x3115). Unlike the old FAX, the HP 3150 does not have a voice announcement feature. Instead, a series of beeps will be heard over the ATF PA when a FAX arrives.
Copying & scanning: New HP 3150 Multifunction also serves as a plain-paper COPIER and can scan directly into ATFSERVER1. The old scanner PC is now located in the new User's room (820 front area) for copying & scanning as before, but now has a dedicated printer.
Please contact Karl (x3116) or Marcus (x5238) for further info.

Building 820M amenities:

1) The PA system has been installed & tested in 820M rooms 14, 1, 2, 8 and the conference room. It uses the same 644 extension, so whatever is announced at 820 will be heard in those 820M rooms (except for the control room hand mic). The 820M hallway and other rooms are not affected, as requested by other occupants;
2) The refrigerator and food storage cabinet are installed in the conference room; The ATF microwave is currently in the new user setup area;
3) An old PC has been installed in the conference room for general web access and "Net-meeting" capability;

New Experiment Control Room Expansion:

The Control Area dedicated to user experiments in the Control Room got a big boost. The evacuation of all user equipment from the ATF Control Room to the new storage area (see above) makes way for four new 19-inch racks and substantial table space. Users will then have more room in which to run their experiments and mount essential diagnostic equipment. Simultaneously, other groups can work on their hardware in the set up area without conflict. Users with special requirements (power, cable lengths, LAN, etc.) should contact the Users Coordinator Vitaly Yakimenko.

1) The table for the control room has arrived. The 19" racks are expected sometime at the beginning of December. Experimenters are advised that they have less than a week to move equipment out of the control room;
2) The helium supply line for the Exp Hall has been installed & leak checked (ready for MINOS). Its primary purpose is for beamline leak-checking and it will eliminate the need for wheeling an entire helium tank into the hall. The nitrogen boil-off supply line is awaiting the arrival of plumbing parts.

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Safety and Operations (REPORTED BY XIJIE WANG)

1 Work permit for radiation shield and interlock system: An NSLS notice on this subject was distributed and discussed. For the ATF in particular, all interlock related work and permits must obtained through the NSLS interlock group. No ATF personnel may work on interlocks, or modify any interlock. If work affects the ATF radiation shielding, a permit can be obtained and approval is by ATF safety representative Mark Montemagno.
2. All experiments should check their compliance with the safety regulation. Particularly the radiation activation check for any thing that may have been exposed to the e-beam in the experimental hall.
3. ATF user coordinator: Dr. V. Yakimenko is now the ATF User Coordinator. I urge all ATF users to contact him or me if help is needed. Please leave the two technicians alone so they can proceed the jobs they were assigned.
4. ATF BLOSA trainer: I have asked both Vitaly and Mark to become ATF BLOSA trainers.
5. Action for Fast detector experiment laser safety violation: The committee on the laser violation of the fast detector experiment has submitted its report. ATF action plan:
A. Modify the ATF BLOSA form to insure all future users aware that, all modification on the experiments must approve before the operation.
B. All people working on the fast detector experiment obtain new BLOSA and laser training before work can be resumed.
C. Fast detector must resubmit their experiment approval form.

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