Thanks to all the contributors to the report.
The Laser Advisory Panel (reported by Ilan Ben-Zvi):
The panel met on Monday and Tuesday (March 15, 16). The participants
were:
Jim Chang, Lawrence Livermore National Laboratory, (panel member)
Andrew Cook, Brookhaven National Laboratory, (panel member)
David Meyerhofer, University of Rochester, (panel member)
Howard Milchberg, University of Maryland, (panel member)
Dinh Nguyen, Los Alamos National Laboratory, (panel Chair)
James Wishart, Brookhaven National Laboratory. (panel member)
Marcus Babzien (ATF)
Ilan Ben-Zvi (ATF)
Igor Pogorelsky (ATF)
Triveni Srinivasan-Rao (Instrumentation Division)
Xijie Wang (ATF)
Li Hua Yu (NSLS)
Vitaly Yakimenko (ATF)
Eric Mottay (B.M. Industries)
Ted McMinn (Cutting Edge Optronics)
Dave Kemp (Positive Light)
Kobayashi (FESTA Japan)
The discussions were very good and many new ideas were proposed for
improvements of the ATF laser in the short and medium term as well as
ideas for future laser development aimed at service of the next generation
high-brightness electron guns. The report of the panel will be distributed
as soon as we receive it.
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HGHG
Experiment status (Reported by Erik Johnson and Adnan
Doyuran) |
Adnan Doyuran and Erik Johnson worked on characterizing the mirrors
and came to the conclusion that only number 3 was a really bad mirror.
By refocusing the alignment laser we discovered that the first mirror
was OK, just over filled with the focus was too far down stream. Tony
Lenhard remanufactured some Si surface mirrors, Adnan picked out the
best one by looking at it in the laser lab, and Mike Lehecka substituted
the mirror for us onto the number 3 probe. Erik and Adnan also removed
monitors 1,4,and 5 and remounted them to get the squirm (from realignment)
out of the bellows. Number 3 was mounted and aligned. All four of the
probes taken out were recleaned. It seems that there was dirt on the
inside of the windows, and that was giving image artifacts. Also when
they looked at the probes last week they found that the number 1 window
had a crack in it which was not leaking, but worried them. Tony Lenhard
modified a stock pyrex window which was substituted it for the cracked
one. Mel and Walter from the vacuum group helped Erik install the modified
probes. The outer mirrors were installed and the images adjusted so
they were on the center of the video screen. The actuators all register
nicely now, and Xijie exercised them and checked that the signals were
getting into the ATF video system correctly. Once the laser was focussed
in the center of the wiggler all the images looked pretty good, although
Adnan found fringes that evidently come from the ND filters on the camera
systems. He cleaned all of the external optics, which helped reduce
scatter, but the fringes did not go away entirely. It is speculated
that the fringes were always there but unobserved due to the condition
of the mirrors until this upgrade. Now the mirrors look very good. Hopefully
the monitors are now ready for use.
More items about the HGHG experiment are provided as part of the facility
report below.
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Dielectric Wake Field Experiment
(Reported by Xijie Wang) |
The first phase of the Columbia-Yale Dielectric Wake Field experiment
has been completed with another run this week. The microwave modes (12
modes, up to 20 GHz) were measured and data analysis is in progress.
Unexpected sidebands were observed and this issue will be investigated.
The device will be removed from the beam line in preparation for the
installation of the VISA experiment. It will return at a later time
for the next phase of the experiment.
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Compton
experiment status (reports by Igor Pogorelsky, Vitaly
Yakimenko and Xijie Wang) |
The first installation of US-Japan collaboration Compton scattering
experiment in beamline #1 was completed in two days. This was a proof
that quick changes between the Compton and STELLA experiments are practical.
The final walk through of the experiment by the NSLS Beam Line Safety
Committee was made. A radiation fault study was performed on Wednesday.
The neutron level neutron was measured at 0.2 mR/hr near the door of
the FEL room to the experimental hall. Under fault condition 4.2 mR/hr
X-ray was detected at the same door’s up right corner. The experiment
was cleared to run.
During two one-day runs of the Compton experiment the team made system
debugging, rough alignment and synchronization of the electron and CO2
laser beam. The 500 pC electron bunches have been focused at the interaction
point to the spot with "sigma" less than 100 um. About 0.5
GW "donut" shaped laser beam was focused at the interaction
point by parabolic mirror with the 15 cm focal length.
The Compton scattering signal at 0.2 nm wavelength has not been observed
as yet. This requires fine tuning of the time synchronization and spatial
overlap of the electron and laser beams. This work is in progress and
will be continued next week. New tune for Compton run was established
with required e-beam size. (Noise level 10mv-50mv, expected signal level
> 0.5 V)
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VISA
Experiment status (reported by George Rakowsky) |
Magnetic shimming of Undulator Section #4 was completed. Sections #3
and #4 were set up end-to-end on the pulsed-wire bench, coupled together
with the phase-adjusting mechanism. This coupling introduced some friction
between the sections at the contact between the ball-bearing tip of
the NRC adjuster and the aluminum bracket on which it bears. This resulted
in small but noticeable (few microns) hysteresis in transverse magnet
adjustments. The friction was reduced to a negligible level by adding
a Macor glass plate over the bracket.
Shimming across the joint was completed for both X and Y trajectories
in normal orientation. The results are shown in the scope image below.
Both sections were then rotated 90 degrees and re-centered on the wire.
The Y trajectory (with wire sag eliminated) was found to be satisfactory
as well, with less than a wiggle amplitude deviation peak-to-peak. Repeatability
of locating the magnetic center of two sections at a time is still +/-
5 um. Some additional measurements and documentation are being done
for use in our PAC99 paper and for a talk at the Workshop on Future
Light Sources, April 6-9 at Argonne.
Hewlett-Packard Service traced the problem in our interferometry system
to a defective cable, which is being replaced. We expect the unit back
in the lab soon.
Aaron Tremaine has arrived at BNL and is settling in. Robert Ruland
reports that the fabrication of the alignment rail system has been completed
at UCLA shops. Assembly at SLAC is starting next week. He expects to
arrive at BNL April 12 to resume interferometric measurements of the
magnet sections and begin the trial installation of the alignment system
on the VISA table. He also reports substantially improved repeatability
of the wire finders, after replacement of the on-board translation stages
with higher precision units.
The enclosed scope image shows the trajectory in VISA Sections #3 and
#4, after shimming in the area of the joint.
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Various jobs (reported
by Bill Cahill) |
Faraday Cup for the Compton experiment was assembled and installed
in beamline .
Faraday Cup shielding was built and approved for preliminary usage
following fault test.
Terminal board for use with 30A p.s. installed and connected.
Fpop1 modified and reinstalled in tunnel.
Gap control on HGHG micro-undulator refitted to read continuos position.
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Hall Probes (reported
by Vitaly Yakimenko) |
Hall probes were installed and tested in the 9 quadrupoles in the high-energy
beam tunnel. The measurement noise issue was addressed. (Current noise
level is 0.5 % peak to peak). The implementation of the hall probes
measurement in the tomographic recovery of the phase space would reduce
required acquisition time from 20 to 3 minutes. A discrepancy between
quadrupole current setting, readback and hall probes reading is under
investigation.
Computer and control system
(Reported by Robert Malone) |
Control room:
Software/operator interfaces for new 30A power supplies completed and
tested.
Software installed/tested for new PC in control room (replaces failing
X-terminal) Operator now has additional workstation with same capabilities
as main console.
Beam line 1 (STELLA):
Software / operator interface installed for new stepping motor control
of x/y axes for laser mirror near GT1.
Software / operator interface updated for new magnet power supply reassignments
(GQ5, GQ6, GQ10, GQ11, GQ12, GQ13) All requests for control system assistance
to STELLA experiment as outlined in Kusche’s memo of 1/2/99 have
been completed.
Beam line 2 (HGHG):
Gap control for mini-undulator:
Problem with hardware interface for digital pulse count has been corrected
(wiring problem). Operator interface for gap adjustment now operational.
Fully open/fully closed can be detected, but precise position can’t
yet be determined (see next item):
Mechanical adjustments made to LDVT analog position readback system
so it now registers over full range of gap travel. (Previously, only
registered over about last 20% of travel.) Software testing / calibration
in progress to complete analog readback for operator display. Once finished,
this will complete all gap control tasks.
Software / operator interface installed for new pop-in monitors:
IPOP1.5 (at mini-undulator), IPOP2.5 (before Cornell wiggler)
Video switching modified accordingly.
Software / operator interface installed for new stepping motor control
of x/y axes of laser mirror at head of beam line 2.
YAG Laser
status (reported by Marcus Babzien) |
3/12: A quick study of laser beam exiting the gun was performed by
collecting the light at the exit port and directing it to the streak
camera in the gun hutch. Only the main laser pulse was observed in a
time scale from the pulse width to 3.6 ns, and down to a magnitude of
about 2% of the main pulse.
3/15-16: ATF Laser Committee meeting convened to discuss current ATF
laser short and long term improvements, and future drive lasers. No
laser operation Monday.
3/17: System operated for Compton scattering experiment > 12 hours,
with realignment required in the afternoon.
3/18: Morning spent aligning and diagnosing beam distortion in gun
hutch. Dirty optics found and cleaned, restoring beam profile. In the
afternoon system was realigned and operated through the evening for
SDWA experiment. 3/19: Operation for Compton scattering experiment.
Electron gun (reported by Xijie Wang):
The new Mg cathode returned to the laboratory and was machined. Some
defects are visible at the 1 inch edge. It is now undergoing vacuum
tests. We prepare to install it at the week of April 5 if conditions
permit.
Measurements of the double pulse as a function of the laser position
on the gun cathode and as a function of the laser to rf phase are attached
as Word files:
The double pulse with the laser spot moved 2.5 mm from the center of
the cathode (BMP file):
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Schedule (reported
by Xijie Wang) |
Week of March 22, 1999
Monday, March 22
8:30 AM - 1:00 PM: RF system studies, Montemagno.
Laser alignment and Studies: Babzien.
1:00 PM - 9:00 PM: HGHG Experiment, physicist Yu, Operator Montemagno.
Tuesday, March 23, 1999
9:00 AM - 5:00 PM: Compton Experiment, Physicist Pogorelsky, Operator
Cahill.
Wednesday, March 24, 1999
9:00 AM - 5:00 PM: HGHG Experiment, Physicist Yu, Operator Harrington.
Thursday, March 25, 1999
9:00 AM - 5:00 PM, Compton Experiment, Physicist Ignore, Operator Cahill.
Friday, March 26,
9:00 AM - 5:00 PM
Prepare for YAG laser room Chiller/HVAC work, Babzien, Harrington and
Cahill. Install new modulator solenoid, Montemagno.
Week of March 29, 1999
PAC 99, Monday through Friday
Mon-Friday
YAG room chiller installation, Babzien and Cahill.
Klystron insulation, Cahill.
Friday, April 2, 1999
ATF Clean up for PAC 99 tour: Cahill
Saturday, April 3, 1999.
12;00 PM - 3:00 PM, PAC 99 tour, Wang, Yakimenko, Pogorelsky, Kusche,
Malone,Yu
Week of April 5, 1999
Monday - Friday: ATF Chiller/HVAC work and Klystron insulation.
1. Remove wakefield experiment.
2. Reinstall Stella spectrometer.
3. Install new laser port window for the RF gun and new cathode (if
components are ready).
4. Test of new laser oscillator.
Electron Beam profiles for three different laser positions:
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