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Site Details ATF Newsletters 
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2000 ATF NewslettersJan | Feb | March | April | May | June | July | Aug | Nov | DecMarch 10 | March 24 | March 31
Greeting everybody, The ATF entered an unscheduled shut down this week when
a modulator high-voltage power supply AND a Pockels cell power supply
failed. Emergency repairs are in progress. Before the shutdown we had runs of STELLA, the Ultra-fast
Optical Detector and longitudinal tomography. In addition we have the
usual collection of progress reports from various experiments and the
facility. Ilan Ben-Zvi.
During the period of 2/28-3/3, the STELLA Experiment had
two days planned for laser alignment and three days for electron beam
tuning and interaction studies.
Murphy’s Law seemed to be in effect, however.
The complex laser alignment of the ICA system required more time
than anticipated. Then, the
first check of the e-beam transmission through the ICA gas cell revealed
the need for adjustment of the cell’s alignment with respect to the last
quadrupole triplet. The first
test of the new VOx target system with the ATF’s GW CO2 laser revealed
problems that forced a redesign.
Finally, by the last day of the run, equipment problems with the
linac brought any further e-beam interaction studies to an end. Nonetheless, the ATF-STI team made important progress:
the laser alignment is nearly finalized, the gas cell and the rest
of the beamline are aligned, and the VOx target has been replaced with
a fiber cross BPM. During this past week, other improvements to the laser alignment
process, fiber cross BPM, and STELLA delay line have been made.
Next week’s runs (only two days) will include further e-beam studies
using the Smith-Purcell BPM’s to improve the STELLA tune, testing the
new fiber BPM, and achieving rough synchronization of both beams at the
ICA cell.
We slowly pumped down the system and the vacuum looks good.
We are going to turn on the ion pumps on Friday and should have vacuum
ready by our next run day, March 17. The BPMs and detectors need to be setup and will be done
by the end of the weekend and will be ready by our next run. After pumpdown, it was found that 5 out of the 7 pop-ins
are now making contact with the undulator. We pumped on the system as
slowly as we could to prevent movement which apparently didn’t work (none
were touching before pumpdown). A smaller design (in the vertical dimension)
is needed and being worked on for implementation during the next shutdown. The
alignment lasers (800nm &566nm) were aligned as best as could be done.
There is much instability in this system (vibrations, thermal drift,
air currents, mirror pointing resolution) and the alignment lasers are
only to within 100um of the magnetic axis. We are currently evaluating
what needs to be done in order to attain the alignment lasers to be within
20um of the magnetic axis. As long as the stability is good enough, guiding
the e-beam to the alignment laser is possible, but will take more time
than if it was within the 20ums. The more sensitive cameras have arrived and we are working
on a plan to implement them into the BPM system. These COHUs are bigger
than the original Hitachis and there is not much room on the table so
minor modifications will be needed. The red-heading was been done for the transport. We are
waiting for the materials to enclose the transport to arrive. Once here,
hopefully by the end of next week, we will finish the transport for the
radiation out the end of the undulator
to the FEL diagnostics room.
Recent runs, dedicated to the detection of the ATF beam
bunches through the electro-optical effect with poled quartz optical fibers,
were unsuccessful. Although
the best fibers we’ve produced have electro-optical coefficients measured
to be two orders of magnitude smaller than LiNO3 crystals, they were calculated
to be adequate for characterization of the ATF beam. Their primary virtue
is that they are quite inexpensive compared to LiNO3 crystals. We have redesigned and installed our detector package which
now contains the optical elements other than the laser and photodiode
detector in the beam line vacuum and to couple the output light to the
photodiode through a multimode rather than a single mode polarization
maintaining fiber. Our March 8
run was devoted to further studies of electro-optical crystals, including
rise time determinations with faster oscilloscopes and with the goal of
eventually employing a streak camera with visible light. We were able
to reproduce earlier results by observing both the polarization dependent
electro-optical signal with the ATF beam approximately 5 mm from a LiNbO3
crystal and the polarization independent attenuation of the laser light
with the beam incident on the crystal. Although some useful data was obtained
the run ended early with the failure of the ATF modulator power supply.
A paper describing our previous results with LiNO3 was submitted
to Nuclear Instruments and Methods in Physics Research A.
We tried the longitudinal tomography beam study on March
7th 2000 and we had planned to measure the longitudinal phase
space distribution with various laser energies (=various charges) and
same rf-gun phase. By changing
the power of YAG laser, we will be able to observe a longitudinal phase
space effect in the rf-gun. The setup at the ATF, following the pioneering work at Stanford
[Crosson, E. R., et al, “A
Technique for Measuring an Electron Beam’s Longitudinal Phase Space with
Sub-picosecond Resolution,” in Micro Bunches Workshop, AIP Conference
Proceedings 367, 397-405 (1996)], is shown below: http://nslsweb.nsls.bnl.gov/AccTes/R0/3_10_long_tomo_setup.htm The longitudinal phase space reconstructed image, the first
measurement of its kind for a photoinjector, is shown below: In the last beam study, at some point the connection between
the personal computer (Mathcad) and main database system of ATF froze.
I didn’t take data. Bob guessed a problem in the taking of a image using
grabber system. In my Mathcad
program, I didn’t stop the grabber system at the time of saving the image.
(I used the grabber system in continuous mode.) So I modified the Mathcad
program using single shot mode of the grabber system. I need to check
this program. At the next beam test, we will try to observe the longitudinal
space charge effect in rf-gun by changing current at constant gun phase.
HGHG Experiment / Facility: Software to read the new diode array diagnostic has been
completed and tested as far as possible without real signals.
This system uses our standard KSC 3516 scanning ADC but strapped
for external triggering. Users must supply a TTL pulse to initiate analog to digital
conversion of the unit’s 32 channels.
Software will collect and display these values on each ATF rep
rate clock pulse. Next week,
with M. Babzien and R. Nawrocky, we should be able to incorporate the
sample and hold hardware for final testing of the system. A Mathcad program was developed to measure various e-beam
parameters for the Weekly report. The program will be expanded as conditions
permit. The output (in PDF format) is at: The file provides the charge vs. phase scan, charge vs.
laser energy, quantum efficiency, maximum charge, charge at operating
phase, etc. Report from previous week: The new circuit breaker panel
for additional power was installed by NSLS Electricians and is now ready
for service. Most of the week was spent fabricating the new linac temperature
control station which will be located below the linac klystron. This will
be an ongoing task as parts that have been ordered will be installed until
the system is complete. Assistance was given to the HGHG Experimental
Group involving small machining and other various tasks. Bob Harrington
has assembled a test dock in order to evaluate a scheme for regulating
the temperature for the RF gun. The set-up is located in the YAG lab and
is undergoing analysis. This week started out upbeat and went downhill quickly.
The initial problem started with the Linac stability. It didn’t take long
before we realized that the linac modulator high voltage power supply
was failing and as predicted, according to Murphy’s law , died. As the
newly ordered Maxwell power supplies have not yet arrived, a quick fix
was to borrow the spare Spellman power supply from NSLS. This too had
failed upon installation. The next resort was to install the last remaining
spare from NSLS, alas, this was also a dud. Being dead in the water, the
ATF’s original power supply was hand carried to Spellman Electronics in
Hauppauge for emergency repair. We should know the diagnosis by Monday.
As this was not enough of a setback for operations, we were informed of
a situation involving the YAG laser system whereas the Pockel cell high
voltage power supply failed. After investigation, we found the bad high
voltage board and contacted California for emergency repair. The unit
was also hand carried for immediate shipment and hopefully will be back
by early next week. In the meantime, we are installing an additional water
controlled temperature stabilizer coil for the rf gun. Assistance was
given to the CPOD Experiment and several ion pump holding power supplies
for HGHG were built for easier pumpdown. The monitor stand for HGHG diagnostics
is being installed in the Experiment Hall and we still had a little time
left over for clean-up. All in all, a busy week! Following topics were discussed at this afternoon engineering
meeting: 1. Don
Davis will start work at the ATF next Monday on the CO2 laser under Igor
Pogorelsky. Bill Cahill will be response for tracking his job assignments.
If VISA needs him, Igor must be consulted. 2. Modulator
power supply: we are pushing on two fronts, one is get new one delivered,
and other one is to fix the old one. 3. Yag
laser Pockel cell power supply: we have shipped the whole unit to the
manufacturer by express mail. Marcus will work with Bob Harrington to
improve the YAG laser table optical layout. 4. We are
installing a new cooling system for the gun. It will be tested next week. 5. TW CO2
laser system: John and Igor reported that, a plan for fix the TW laser
cell is in place. Igor will prepare a detail plan for CO2 laser operating
at 30 ps (FWHM) and 10 J energy. 6. Schedule: Please submit your running time request for April, May and first half of the June. We also plan to have a one week shutdown in the late April or early May to install new laser system if everything works out.
Last Modified: December 3, 2007 |
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