2000 ATF Newsletters
May 5 | May 19
Greetings,
The new exciting developments: Staging experiments
have started in STELLA and gain observed in VISA.
Ilan Ben-Zvi.
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STELLA
Experiment (REPORTED BY WAYNE KIMURA AND KARL
KUSCHE) |
The STELLA experiment ran for 3 days this past week and accomplished
a number of important objectives.
We successfully commissioned the new second permanent-magnet
IFEL, which was installed last week to replace the ICA gas cell
as the accelerator stage for the experiment.
We also reestablished modulation in the first IFEL (i.e.,
prebuncher), which is located upstream from the second IFEL.
The first figure shows a typical e-beam energy spectrum
with no laser beams driving the IFELs.
(Energy dispersion is on the abscissa.) The intrinsic energy spread
is approximately 0.1% (1-sigma) with the mean energy set to 45.6 MeV corresponding
to the resonance energy needed for the first wiggler.
5_5_STELLA_Laser_off
The second figure shows the energy spectrum from
the first IFEL (i.e., prebuncher) with no laser driving the second IFEL.
The double peaks predicted by theory can be clearly seen in the
picture and are centered symmetrically about the mean energy (c.f., laser-off
figure).
5_5_STELLA_IFEL1_only
The third figure shows the energy spectrum from the
second IFEL (i.e., accelerator) with no laser driving the first IFEL.
In this situation the second IFEL behaves like a modulator.
However, because the second wiggler is designed for a slightly
higher resonance energy (46.3 MeV), the model predicts the modulation
spectrum should be slightly offset from the mean energy point in the positive
direction. Indeed, comparing
the first and third figures we see there is a positive offset.
5_5_STELLA_IFEL2_only
Next, the two IFELs were operated together.
This is the first time two IFELs have been staged together.
(During our last run in March, we demonstrated for the first time
staging together of an IFEL and ICA system.) The resultant energy spectrum
was measured as a function of the phase delay between the laser beam driving
the first IFEL and the laser beam driving the second IFEL.
(This is the first time we tried using the fine stepper motor on
the trombone delay line, which is capable of 0.4 microns/step.)
Copious amount of data were collected during the
run. The CO2 laser was shot
over 400 times. Over 140
energy spectra were collected. We
probably set a new record for the STELLA experiment on the amount of data
obtained during one day.
The model predicts that the energy spectrum should
contain specific features, which change in shape and position in energy
depending on the phase delay between the two IFELs.
The energy spectra when running both IFELs certainly did change
in shape, but not in a manner predicted by the model. We will be analyzing the data and exercising the model during
the next weeks to better understand what occurred during the experiment.
Several factors could be causing this disagreement.
First, the model is an idealized one and does not include 2-D effects.
This latter point may be important because during the experiment,
the e-beam transverse dimensions were comparable to the laser beam focus
size inside the wigglers and were not always symmetric in shape (i.e.,
the e-beam transverse profile was highly elliptical at certain locations).
The amount of effective laser power being delivered to the second
IFEL may be less than needed to clearly see the trapping of the microbunch
[e.g., the modulation seen for the second wiggler (i.e., the third figure)
is about a factor of 2 less than expected.] There are indirect clues that
we may be still undermodulating the first IFEL, which might mean poor
microbunching is occurring at the second wiggler.
The next major STELLA run is scheduled for May 16-19,
2000. Some hardware changes
will be made to improve our ability to better focus and coalign the e-beam
and laser beams inside the wigglers.
Vitaly will also have a 1-day run on May 2 to improve his tune
of the e-beam through the wigglers in order to have more symmetric and
smaller e-beam profiles through the wigglers.
Work will continue on the IFEL/IFEL model to help us better simulate
the actual experimental conditions.
Following the run:
1) New
wiggler on beamline #1 was realigned via HeNe, pop-in cameras calibrated
for proper ND filter attenuation for centroid determination, and beam
studies followed to improve tune.
The beam profile downstream of the new wiggler was originally though
to be distorted due to a problem with the wiggler itself, but a short
run today proved otherwise and obviated the need for shimming and/or magnetic
measurements. In fact, the
spot size and position held to within a fraction of the beam diameter
when the wiggler was lifted out of the beampath.
2) At
STI, preliminary simulation results suggest that the e-beam focus size,
energy spread, and emittance (beamline #1 tune) may have been too large
during last week’s runs for optimum bunching, thereby making it difficult
for staging effects to be observed.
Further investigation is needed, and group discussions will be
held next week.
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VISA Experiment
(REPORTED BY AARON TREMAINE) |
Friday 4/21/00 we ran from 9am to 2am.
XJ started at 9 am with laser profile and e-beam
profile studies in the tunnel because there was observed structure in
the e-beam profile. When
we ran beam through the undulator (2pm), we studied the e-beam trajectory
relative to the alignment laser. Since the horizontal was studied last
time we focused on the vertical trajectory through the undulator. As expected
it was much easier to contain. At first the peak-peak was ~1mm.
After about an hour of upstream steering magnet changes, the peak-peak
was found to be <200um. This correction is repeatable and we made this trajectory correction twice during the run.
Detector vs. Faraday cup measurements were made.
Better collection of radiation could possibly help.
Since the detector is inside the experiment hall, x-ray background
noise adds error to the lower charge measurements More information, including
graphics, can be seen in the following pdf file:
4_24_visa
status
Thursday April 27 was a VISA run day. XJ
started tuning the beam at 9am, and we sent beam through the undulator
at noon. The most stable time for the system is after 6pm. XJ, Alex and
I called it an early evening and shut down at 10:30pm.
The beam was run @ 70.9MeV with an energy spread
of <.3% full width. We
were able to correct the vertical trajectory to within 100um of the alignment
laser. The best we could do with the horizontal was peak-peak of about
1.8mm.
Detector vs. faraday cup measurements were made,
and the plot appears to be non-linear- an indication of gain.
A shutdown will occur the week of May 8 in which
another interferometer alignment will be done. I will send out a schedule
for the next two weeks.
More information, including graphics, can be seen
in the following pdf file:
4_28_visa
status
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Technical
Operations (REPORTED BY BILL CAHILL) |
Monday’s Maintenance Day proved interesting in the
never ending rf jitter scenario. Most of the complaints concerning beam
jitter were geared mainly to the linac. Marc spent the entire day troubleshooting
the low level system in both modulator controllers and found several “sma
“ connectors loose in the gun section. After a complete shakedown, the
jitter problem has basically disappeared. It
looks as if the problem was actually in the gun area and somehow
masked itself. We learn something every day. A problem was resolved with
the YAG Pockels cell high voltage cable and a defective low level power
supply is suspected in regard to a mirror motor on the HGHG line. The
experiment is working around it until we can afford the time to repair
it. Bob Harrington has been trying to fabricate and complete the water
system for the YAG amplifier and pre-amplifier due for installation in
next week’s shutdown. We have come to a complete standstill due to the
lack of parts and the lack of cooperation from the central stock system.
As the stockrooms only open on half days, the delivery schedule has shifted
from ˝ day to 3 days. Due to the lack and elimination of the mass majority
of parts, everything has to be outsourced, taking up valuable time for
ordering. This is presenting a big problem.
Beamline #3 has been bled up for VISA and “Fast detector” work,
a clean-up of our machine tools in 820A was
needed at the request of DAT and as always, aside from mandatory
training, provide support for ATF operations.
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Friday
Engineering Meeting (REPORTED BY XIJIE WANG) |
Friday 4/28/2000:
1. ATF
schedule: next Tuesday HGHG run will for STELLA, and Friday beam studies
requires ATF experimental hall interlock.
2. May
8th ATF shutdown: due to delay of the parts, both oscillator
and linac water will not be ready for the shutdown. Two other jobs will
be scheduled. One is the laser amplifier water system (Harrington), other
is to test both low level and 1 KW RF system (Mark). Beam testing is scheduled
for Thursday (May 11) and Friday (Yakimenko)
3. YAG
laser work: Mark should fix the Pockels cell cable first thing Monday,
and check the heater power supply for the amplifier.
4. CO2
work: Mark will make grounding cable for the new CO2 charging power supply.
Don will work for VISA from May 4 to May 15 (inclusive), once discharge
cell is back to ATF, both Don and Harrington will work on the CO2 after
shutdown.
5. VISA
request exclusive access from Friday May 12 8:00 AM to Monday (May15)
12:00 PM.
6. Both
VISA (including matching section and beam pipe after the undulator) and
fast detector request vacuum bleed up on Thursday (May4, Harrington).
Friday 5/5/2000:
1. ATF
facility safety and operation procedure: several incidents took place
this week that require immediate action. One is that
the ATF experimental log book disappeared from control room until
this afternoon, the other is that the check list and operations log were
not filled, and control room door left open overnight.
All ATF operator and duty operator will be re-trained next Friday
1:15 PM, and no ATF beam operation will take place until that time.
2. Next
week ATF shutdown: Mark will check all RF connections, tune up both 1
kW amplifiers, and install new capacitors, Harrington will help on the
linac water system, and TW CO2 cell hydro-testing.
3. Fast
detector requested to install a new stand, Harrington will check to see
how safety looks.
4. Harrington
suggests make sure yellow tag will attached to the vacuum valve if one
side is on the air, I agreed.
5. VISA:
Don will work for VISA next week full time, VISA exclusive access start
Friday, and end next Monday. STELLA laser alignment need to work in the
experimental hall next weekend, I think they should be able to accommodate
each other. I asked Marcus and Alex to put up signs for SLAC alignment
laser this afternoon.
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ISM Feedback
and Improvement Corner (ILAN BEN-ZVI) |
Thanks to Xijie Wang and Eva Rothman, the ATF users
training has been standardized as BLOSA training. A form has been placed
on the web at:
http://nslsweb.nsls.bnl.gov/Training/ATF/atf-blosa-form.doc
All current ATF users have been retrained by Xijie
under the new format, and the list of trained users, maintained by Eva,
is also on the web at:
http://nslsweb.nsls.bnl.gov/Training/ATF/atf-blosa.htm
Xijie Wang, Bill Cahill and Marcus Babzien are the
qualified ATF BLOSA trainers.
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Last Modified: December 3, 2007
Please forward all questions about this site to:
Vitaly Yakimenko
|
