Greetings all,
The good news of the week is that the ATF beam brightness as measured
is already better than what is specified for the HGHG experiment (see
below), at 100 A peak current and emittance better than 2 mm-mrad.
We still have to replace and or relocate components that are known
to be problematic in the laser transport system (gun hutch optics)
before we establish VISA brightness levels. That will take place in
the next couple of months.
This week the regular users program continued with two days of HGHG
and two days of STELLA runs. The laser stability continues to be excellent
without any alignment for the whole week.
Next week there will be no weekly report. The week will be dedicated
to placing the laser oscillator in a more stable location on the table
and isolate it with a highly regulated temperature enclosure, various
maintenance issues and preparation for the VISA experiment.
Ilan Ben-Zvi.
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HGHG
Experiment (Reported by Adnan Doyuran) |
This week on Tuesday we did a trajectory study. I started with the
vertical trajectory. First I roughly aligned the with respect to the
He-Ne laser using monitors 1 and 4. Then we ran the trajectory correction
program. The program corrected the trajectory to within +/-15-20 pixels
accuracy (1 pixel is about 10 microns). When we run the program repeatedly
it got better and reduced the error to +/-10 pixel accuracy. Realignment
of the He-Ne laser also helped, thus I ordered a motorized mirror
mount for remote steering. Following that I followed the same procedure
for the horizontal steering. After several trials, I still couldn’t
get rid of the steering produced by a change in the focusing strength.
This may be because of a measurement error resulting from the changing
beam size due to the variation in the focusing.
The next test was a measurement of the steering due to the mini-undulator.
We recorded beam before and after the mini-undulator with the gap
fully open. Than we closed the gap and recorded the movement of the
beam on IPOP1.5 and IPOP2 and Wiggler1.
IPOP1.5 changed horizontally 9 pixels, vertically 4 pixels. (Calibration
is unknown yet)
IPOP 2 changed horizontally 4 pixels, vertically 4 pixels. (Calibration
is unknown yet)
Wiggler1 changed horizontally 25 pixels, vertically 9 pixels (Calibration
is about 10 microns per pixel)
This data requires analysis and discussion in the group. On the Thursday
run we changed the energy to 41.5 MeV. We tried the trajectory study,
but realized that the program is calibrated for 49.9 MeV and requires
new matrix elements at the new energy. Anyway we took data for trim
magnets at this energy because we’ll need this data. I recorded
positions of the beam at each monitor for different currents at trim
magnets.
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STELLA
Experiment (Reported by Karl Kusche for the STELLA
team) |
1) The following progress/results came from Wednesday’s beamline
#1 beam studies run:
- Radiation survey completed, no leakage out of Experimental Hall
observed;
- Quad rotation issue - vertical line on spectrometer indicates
that present
45 degree orientation is satisfactory for the foreseeable future;
- Beam transmission to the end of the line still needs improvement
(so far,
~5-10pC, 25-50 max, out of ~200pC has been delivered to the spectrometer);
Vitaly will perform matrix calculations for tomorrow’s run to
attempt to eliminate triplet 4 steering;
- Over the next few weeks (taking advantage of the shutdown and
Igor’s absence), we must address two important systems - VOx
target system and CTR optical setup. Karl and Ping will also continue
linac operator training during STELLA runs.
2) The following progress/results came from Wednesday’s beamline
#1 beam studies run:
- Inverse Cherenkov section (radial polarizer system, and gas cell
coalignment) was aligned, and amplified CO2 laser delivered.
- 1 nsec synchronization between e-beam and CO2 laser established
for both IFEL and ICA sections (separately);
- Few hundred MW (estimate) delivered to ICA gas cell, no ICA effect
seen (spectrometer at 8 degree, high-resolution setting)
*
We will try again on the run of June 23.
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Technical Staff Tasks
(reported by Bill Cahill) |
The previously owned ac line conditioner was repaired and tested.
This device will soon be installed in the low level rf to increase
the stability of the system. After extensive troubleshooting, the
phase jitter effecting the gun modulator was found. Modulator noise
was getting into the master phase shifter. The source problem will
be corrected during the upcoming shutdown. The gun modulator PFN was
retuned for flatness in the operating range and now seems stable.
The current zero point for klystron water was recalibrated for better
stability of the thermal drift during extremely hot weather. New hardware
was installed for the linac waveguide phase shifter for computer control.
The beam profile monitor for the VISA matching section was installed
in beamline #3. Electrical and mechanical assistance was provided
for repairs of the Compton target.
YAG
Laser Status (Reported by Marcus Babzien) |
Good laser stability this week allowed reliable and productive delivery
of beam to the gun. The system was only realigned on Monday and the
output energy has not decayed. Shot to shot stability was very good
as well, with 1% rms fluctuations in UV observed sometimes. Also,
yesterday a cylindrical lens telescope was installed in the gun hutch
to produce a circular spot on the cathode without clipping most of
the beam. This allows much higher transmission to the cathode and
over 100 microjoules can now be delivered.
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Beam
Operations (Reported by Xijie Wang) |
1 The planned Monday beam study was not done due to a lost lens shipment.
Cahill get it on Thursday from UPS, and it was installed on Thursday
night. Monday laser energy has peak to peak fluctuation about 10%.
The result of Friday laser cleaning by Wang and Malone was not good
because (a). Laser energy variation form location to location as large
as 10%. (b) Laser Joule-meter drifted with time. The RF gun phase
drift observed on the previous week was traced to the control cable
for jitter feedback system. 2 Tuesday and Thursday were scheduled
HGHG runs. The experiment was mainly used for training and trajectory
studies. A laser phase jump was observed. Several times (lasting a
couple of seconds) the gun RF lost power. The problem was traced to
the gun 1KW amplifier.
3. Wednesday and Friday were scheduled STELLA runs. Some beam jitter
was
traced to the timing jitter from the gun RF system. This problem
was solved
by retuning the RF gun modulator.
4. Thursday evening, following the installation of the cylindrical
lenses, we were able to produce an electron beam with 750pC charge
and edge to edge pulse length of about 10-12 ps. This gives a peak
current of about 100 A. Emittance measurement was not done since it
seemed that half the beam fell out of the laser cleaning area. Please
view the figure June_11_energy_spread
, which shows the beam at the high energy slit with full energy spread
about 0.5%.
5. Igor Pogorelsky and I came in on Saturday around 7:00PM for a
special beam studies. I decided that we must clean the cathode if
we want to measure the emittance. I decided on using a large laser
spot size and clean a large area to overcome the uncertainty of the
laser alignment. The automatic cleaning program did not work because
of large variation of the photo-diode signal. I set up a remote camera
to monitor the gun vacuum, and manually cleaned the cathode by watching
the vacuum. The QE improved significantly. After cleaning, we started
the beam studies. We spent a couple hours on optimizing the beam by
steering the laser on the cathode and through the transport line.
We still observe some non-uniformity of the e-beam profile. We measured
the edge to edge of the pulse length for charges from 500 pC to 800
pC, and the full pulse length again in the range of 10 to 12 pC, which
corresponds to about 100A peak current. We measured the beam emittance
for 500 pC charge using both quad scan technique and two beam profile
measurement. We spend time optimize the beam profile on H-pop1 and
Hpop2 (results shown in June_11_HPOP1_and2
) before the emittance measurement. The measured horizontal normalized
emittance for a 500 pC range from 1.1 to 1.6 mm-mrad using quad scan
technique. A Two Beam Profile Monitors technique gave the number about
2 mm-mrad. In conclusion, we have be able to produce an electron beam
with a normalized rms emittance of less than 2 mm-mrad (more likely
1.5 mm-mrad) with a peak current of 100 A. We will continue to work
on several fronts to improve the beam. The main project we are now
working on: (1) On-line beam characterization, including steering,
matching, and emittance measurement. (2) Improvement of the RF system
reliability. (3) Improve the laser timing jitter and drift. (4) Study
the front end optics and laser alignment. (5) New scheme of wave-front
correction and normal incident optics. (5) Improve the gun vacuum
system so that a good QE will be last longer.
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ATF Schedule
(Prepared by Xijie Wang) |
schedules/atf 99-6
A new schedule for July and August is being prepared.
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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