In this (short) week the YAG oscillator came back from CLEO and was
re-installed. We used one day to re-install the oscillator, one day
for beam
studies, one day for HGHG and one day for STELLA. The YAG laser stability
was exceptional, 1% to 2% rms energy stability in the UV, with outstanding
mode and mode stability.
We are still suffering from humidity problems in the YAG room causing
change in optical component properties and possible permanent damage.
Plant Engineering is working to solve the problem.
Ben Poling and Roger Carr finished a 3 day fruitful stay at BNL,
working on the VISA wiggler.
Communiqué from Argonne: Vadim and his wife welcomed a new son to
the world on June 2, 1999. His name is Phillip. He weighed 5 pounds
and was 47 cm long. He was born at 00:24. Mom and baby are doing well.
(So is dad, he is walking on clouds!)
Ilan Ben-Zvi.
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Magnetic Measurements
(Reported by GeorgeRakowsky) |
VISA:
Roger Carr and Ben Poling, together with the NSLS Surveyors and mechanical
technicians, reassembled and aligned the VISA vacuum box. They also
began assembling the interferometry rails. Brian Fuss and a SLAC technician
will be here next week to finish assembling the alignment system.
One steering coil stand had to be modified to clear an interference
with the alignment frame.
Lorraine analyzed the 90 and 270 degree fiducial data for VISA Sections
1 & 2 and found that the measurement errors are within the error
budget. The main source of error is the fit between the tooling balls
and the sockets on the gauge bar, due to wear of the aluminum sockets.
We will replace the latter with a harder material.
George and Roger Carr examined the impulse response (proportional
to 1st integral of the field) of the pulsed wire in Sections
1 & 2, using a Le Croy scope, which has higher resolution than
our HP scope. Roger will use this data to try to determine dB/B and
dE/E of the beam.
HGHG:
The tilt limit switch and the vacuum pipe touch switch assemblies
are ready, but have not yet been installed. LED’s are being added
to indicate an open limit switch, for diagnostic purposes. The hardware
will be installed and wired in on Monday.
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HGHG Experiment
(Reported by Adnan Doyuran, Vitaly Yakimenko
and Xijie Wang) |
We had a very good round and stable beam. The charge was 200 pC.
We tested
the transition radiation beam profile monitor located in the middle
of the modulator wiggler, and got a reasonable beam profile even
at this low charge. The trajectory was also very good. When we overlap
the HeNe and e beam at monitors 1. and 5. we got a reasonable offset
on >the 2nd, 3rd, and 4th monitors.
Vertically it was perfect, horizontally was >good. Then We ran
Vadim’s trajectory program , vertical with HeNe and >horizontal
without HeNe (focusing only), horizontal trajectory got better,
as expected. We measured spontaneous radiation from radiator. We
got >about 200 mV with 200 pC charge.
For pictures of the beam on the five monitors before the correction,
(electron beam nice small spot, HeNe laser large, ugly spot - we
will fix
that), click on
May_4_hghg_monitor_images
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VISA
Experiment Progress (Reported by Roger Carr) |
Three crates of Robert Ruland’s alignment materials have arrived.
Holes in the top plates for the alignment fixtures that were misdrilled
will be corrected. Also, the trim coil mounts that were placed inside
the alignment fixtures did not fit, and these are being redone.
The vacuum boxes, undulator mounts, pedestals and tables were all
re-assembled this week, and surveyed into place. The mid-point flanges
in the vacuum box are not perfectly square, so they are about 2 mm
higher than the end flanges, and cause the tank to bow up in the center.
This should not be a problem; they have all been located in position
by the survey crew, and all numbers have been recorded.
There is no way in the previous design to re-locate the midpoint
flanges to each other, so ‘Dutch’ pins will be placed between
the flanges to facilitate re-location. Roll has been taken out beforehand,
to about. 1 milliradian, between the two vacuum tanks.
I would add the comment that it is MUCH easier to work on VISA in
building 726 than in ATF, and I hope the system is not placed in ATF
pre-maturely. I hope the optical diagnostics and bpm’s and alignment
laser systems can be thoroughly debugged in building 726.
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VISA Matching Section
(Reported by X.J. Wang) |
The quadrupole magnets and stripline beam position monitors were
installed. The parts and pre-assembled for four beam profile monitors
are now finished, ready to be installed next week. Cameras for the
beam profile monitors waiting to be ordered. R. Carr of SLAC is searching
100 MHz peak sensitive ADC to improve the ATF stripline beam position
monitor for VISA.
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STELLA
Experiment (Reported by Karl Kusche for the STELLA
team) |
1) Beamline #1 was readied for the beam studies run of this Friday
(6/4).
Results of this run will determine if further quad rotation is appropriate.
Regardless of the need to further rotate the last triplet, it was
realized that no further surveying or machined parts will be necessary
for the short-term. Manual rotation, with the help of a borrowed inclinometer,
can be accomplished such that each quad is within +/- 1 degree of
each other (which is acceptable for now).
2) ICA optical system restoration & realignment continues in
preparation for ICA recommissioning during the months of June &
July.
The local STELLA group satisfied the following goals during beamline
#1 run on 6/4/99:
1) Improve e-beam transport through the ICA gas cell (1x1 mm square
windows and 0.6 mm laser shield are limiting apertures; 5-10% of ~200pC
total charge was delivered to end of line).
2) Observe beam distribution on spectrometer BPM (end of line); desired
vertical line on screen indicates that 45 degree quadrupole rotation
is probably OK (will study further next run).
3) Compare YAG single-pulse and double-pulse modes.
4) Operator training.
5) Identify problems (and potential improvements) with imaging, etc.
To be resolved before and during the next run, scheduled for 6/9/99:
- Maximize beam transport through gas cell, and finalize decision
to keep quads at 45 degrees
- Final radiation survey
- Correct imaging problems with GPOP4 (off-center with "ghost
tail") and cell camera (increase light collection)
- Correct imaging problem with BPM7 (reduce background light leakage)
- Prepare striplines (GSL2,3,4)
- Check OTR signal on GPOP4
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Computer Control System
(Reported by Bob Malone) |
1) Debugging continued on the YAG slow drift energy correction software.
A problem was noted where the server program would not respond to
an operator request to disable the correction. This occurred around
every 1 in 90 times the program was tested. After several days of
study, it was traced to a software time delay which did not queue
interrupt requests properly. It has been corrected and final off-line
testing will continue. 2) Software to access the ATF database from
a Mathcad worksheet was tested for the first time with real beam.
All basic operations to read and write the database asynchronously
have been tested and are working.
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Technical Staff Tasks
(reported by Bill Cahill) |
During this short week, we reinstalled the new YAG oscillator. Had
a problem with the YAG preamplifier temperature interlock. It was
found that it had no air intake for circulation. The unit was modified
and now seems to be working well. A TV camera was installed on the
mezzanine to observe the gun and linac phase. This should reduce the
troubleshooting time in case of problems. We tested the RF circulator
for the gun klystron. This component will protect the kilowatt amplifier
in the event of bark-back from the klystron. It will be installed
on Monday. All STELLA discrepancies have been resolved. The trim magnets
have been reconfigured, cooling water to the sextupole magnet has
been installed, video and zoom lenses are complete. The VISA faraday
cup pop-in mirror/lens assembly has been completed and remaining pop-ins
will be available for installation next week. Digital thermometers
have been installed in the RF gun area, the new klystron enclosure
and on the mezzanine. This should help us better control the temperature
and avoid unnecessary downtime. An additional a/c unit was installed
in the control room to reduce equipment heating.
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Installation of beam enclosures for the CO2 laser transport line
between rooms C1 and C2 and work on eliminating gas leaks in the CO2
laser preamplifier and in the terawatt amplifier are still in progress.
The new YAG oscillator is back after exhibition at CLEO 99. There
are a couple of new observations that need to be addressed:
1. The output power is 250 mW as compared to 325 mW before the exhibit
and 375 mW a month ago.
2. A high sensitivity of mode locking due the parasitic optical reflections
from downstream of the oscillator. That results in the 5-10% standard
deviation of the energy after preamplifier. The problem has been eliminated
after realignment of the end mirror in the oscillator cavity and replacing
a polarizing beamsplitter downstream the oscillator. However, there
is not a full certainty that the bad behavior is gone forever and
is not a transient phenomenon that may repeat itself.
3. Another indication that something is not quit right with the mode-locker
is the observed transient phase instability. That appears as periodical
several second long jumps by ~1 ps. Sometimes this jumps are not periodical,
but still reproducible in length and amplitude. Most of the time phase
shows a normal behavior with a slow stabilization drift in response
to a change in external conditions (vibration shocks or temperature
changes). Thermally stabilized enclosure around the oscillator looks
to be necessary to improve the phase stability.
In spite of the mentioned above negative observations, we had a very
positive experience most of the time servicing a photocathode with
the YAG laser beam. Energy standard deviation at all control points
was around 1-2%. Laser profile on photocathode was smooth, quasi-Gaussian
and stable within a few micrometers. (I believe that the pointing
and energy stability will be reported by X.J.) We shall understand
however that the improved stability is partially due to a significant
clipping of the central portion of the laser beam by the iris that
selects a 3.5:1 ellipse out of the whole laser beam.
We will start to use a total laser beam next week upon installation
of a
cylindrical telescope
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Beam
Operations (Reported by Xijie Wang) |
Following is the brief summary of the ATF operation this week:
1. Tuesday: Marcus , Bob and Igor installed the oscillator and realigned
the optics. Amplifier chiller broke down and temporary replacement
was installed. No e-beam.
2. Wednesday: Igor got the laser ready at about 12:00 PM, but both
laser energy and profile were unstable. Igor traced this to a back
reflection which caused oscillator instability. Igor started work
on polarizer isolation at about 2:00 PM, and laser was ready at 5:00PM.
Both laser profile and energy are very stable shot-by-shot. Laser
energy peak-peak varied less than 5%, and rms less than 1%. Laser
centroid rms variation less than 1.5 microns, and spot size rms variation
less than 1 microns for a 1.5 mm diameter laser spot. We observed
laser energy slow drift down about 20% in first hour, Igor increased
the voltage of the pre-amp power supply by 1% and the laser energy
was restored. Phase jitter between the RF and laser on the order of
couple pico-second was observed several times. The RF system was stable
during those times, but laser phase meter was not working properly.
We spend most time optimizing the e-beam. We found the optimal laser
position at about 0.7 mm left, 0.5 mm down, in agreement with May
21 results. The charge was low because half the laser spot is now
located out of the cleaned area. For a charge between 250 - 300 PC,
we measured the rms emittance less than 2 mm-mrad. No bunch length
measurement was done due to jitter. Bob Malone successfully tested
the emittance program, and new MATHCAD interface with ATF control
system. This new tool will greatly increase the ATF on-line modeling
and analysis capability. 3. Thursday: Vitaly and Mark fixed the laser
phase meter. We observed periodic laser phase jumps of 0.8 ps (calibration
maybe off using the e-beam, this should be about a factor of two larger).
Igor thinks this was caused by the oscillator feedback motor. We did
a test - by opening the laser enclosure, a laser phase jump was observed.
By placing a hand gently on the oscillator we observed a phase drift.
This problem should be solved in the week of June 14 when the oscillator
will be placed in its new location directly on the optical table and
the new temperature stabilized enclosure will be installed. A good
laser stability, similar to the previous day, was observed. The HGHG
experiment was started at about 11:30 AM. The beam was stable with
some small laser phase jitter. We observed the RF gun klystron phase
being unstable between 4:00 and 4:30 PM. By 5:30 PM, HGHG finished
its task of the day. We prepared to clean the cathode, but laser pre-amp
shut down due to water over temperature. We traced the problem to
the vestibule temperature rise, caused by AC fan shut down aimed at
reducing vibrations. This problem was temporarily solved opening the
door to the laser laboratory and increasing the air circulation of
the power supply. 4. Friday: 10:30 AM laser was ready with similar
good stability in energy and profile, laser phase jump was observed.
RF gun klystron phase is not stable between 12:00 and 12:10 PM. Following
the Stella run we plan to clean the cathode.
In summary, we have demonstrated this week that both laser and RF
systems are stable under hot weather.
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ATF Schedule (Prepared
by Xijie Wang) |
June 99 schedule
Plans for the June 14 ATF mini-shutdown:
a) Install new oscillator in the final position: John and Bill will
contact Tom White to make sure the Temperature enclosure is ready,
at least bottom part. b) ATF plug door modification for VISA experiment:
Concrete blocks will be poured at a roughly similar size. John and
Bill will meet the plant Engineering people to finalize details on
Monday. c) RF improvement: Mark will test low level and kW RF system
during the shutdown. d) Diagnostics work: Install new ion pump and
change Lpop1. Bob Harrington has to bake out the screen for Lpop1
(one day). This job will wait if YAG laser jobs require his time.
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