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Site Details ATF Newsletters 
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1999 ATF NewslettersMarch | April | May | June | July | August | Sept | Oct | Nov | DecNovember 5 | November 12 | November 19
Greetings to all, This week we held the VISA
Collaboration Meeting. It was a very good meeting. The previous VISA meeting
at BNL took place on January 1998. We had many video conferences in the
meantime as well as in-person meeting at SLAC and UCLA, but this time
seeing the advanced state of the various systems at BNL was invigorating.
We are all looking forward to the installation of the VISA undulator at
the ATF which will start in a little over one week. A photograph of a
small (and pleased) group of participants can be seen next to an undulator
section being measured at the NSLS Magnetic Measurements Laboratory. Left
to right: Jeff Aspenleiter (BNL), Art Toor (LLNL), IBZ (BNL), Claudio
Pellegrini (UCLA), George Rakowsky (BNL) and Vitaly Yakimenko (BNL). The
picture was taken by Max Cornacchia, (SLAC): Ilan Ben-Zvi. 1)
Beamline #1 preparations for the runs this week were completed,
including installation of a new CTR foil (0.25 mil Al) at GPOP4.
Vacuum, leak check, and survey of the line were accomplished. 2)
Vitaly utilized the first run (Thursday) to deliver ~100% of ~0.5nC
at 45 MeV through the new STI wiggler to the spectrometer.
Remember that the ICA gas cell is not installed
at this time. A radiation
survey was performed, giving approval to the restacked shielding at the
end of the line. After the
tune was improved, it was observed that the new wiggler (permanent magnet)
does not cause detectable steering to the beam. 3)
The rest of Thursday afternoon, as well as most of Friday, was
spent aligning a HeNe laser beam through the wiggler.
A problem with the positions of some of the beam profile monitors
was discovered, with respect to the beam axis.
The group decided that the next step for beamline #1 will be to
bleed it up to nitrogen and carefully realign all diagnostics (and the
wiggler bore, if necessary) to the HeNe beam axis, after its overlap with
the e-beam axis has been verified.
The next few weeks of ATF shutdown will provide a fortunate opportunity
for this alignment work. Delivery
of the GW CO2 will follow. 4) Progress at STI Optronics: The ICA gas cell internal BPM has been redesigned and fabricated, which will be used to visualize the overlap of the CO2 laser and electron beams. It consists of a VOx chip on a finger which is mounted onto a translation stage. Accommodations for alignment and heating of the VOx (necessary to visualize the CO2 profile) are included. STI is now preparing to test the VOx with a CW CO2 laser. They have also effected repairs on the encoder mike controller (gas cell laser mirror alignment), which failed during our last week of running in August.
A
valve can be installed before the VISA undulator which will isolate VISA
from the rest of the experimental hall beamlines.
Vacuum testing on the chamber was done with a single 240l/s pump.
With no magnets, the pressure at the far end of the chamber
(with respect to the turbo) was in the 10^-6 range after 6 hours
of pumping. Tests were done with one and two sections and after pumping
for 2 days with 2 magnet sections inside the chamber, a pressure at the
far end of low 10^-5 was measured. We believe with better conductance
and another turbo, when all four sections are installed, we will be able
to get to the desired pressure for the ion pumps to kick in. Robert is coming Nov.
8 and next week will test out the alignment system on all four sections
of undulator. In addition, we need
to mechanically test the BPM pop-in assemblies. A long term solution for
checking the BPMs when inserted has been found. By electrically isolating
the pop-in from the chamber, a simple ohm-meter will tell us if contact
has been made between the pop-in and undulator. XJ has agreed to run
beamline 3 before the installation starting Nov.15.
We need to assemble a working BPM with optics and install it in
the beamline no later than Wed. (Nov. 10) of next week. There were near term
solutions for the BPM mirrors that were discussed at the meeting earlier
this week. Hand polishing
the mirrors will be tried as soon as the holder assembly from UCLA arrives.
It was FED EXed yesterday. This will give us around
2 lambda. We are waiting for the lamda/2 mirrors to arrive. Then the will
be glued to the BPM side mirror and the better of the two will be pursued
for the BPM test next week.
VISA
sections 3 and 4, as well as both wire finders, have been measured on
BNL’s CMM. Sections 1 and 2 are being measured tonight (Friday, 11/5/99).
The accuracy of this machine is 0.0002” (5 um). The biggest discrepancy
with SLAC CMM data is in the wire finders - about 0.006” (150 um)! Discrepancies
in the measurements of Sections 2 and 3 are much smaller. BNL’s CMM measurements
agree with Jeff’s micrometer measurements to within 0.0002”. Closure errors
for Section 3 in 0 and 180 degree orientations are now in the acceptable
range. I believe we have found the smoking gun, although we have not figured
out who pulled the trigger. We can always blame Federal Express, I suppose. At this point, we have
completed fiducialization on Sections 2 and 3, and Sections 1 and 2. Section
3 has been installed in the vacuum vessel with two pop-in assemblies in
place. Sections 1, 2 and 4 will be installed Monday, in preparation for
the alignment exercise. We will have the latest fiducial data for Sections
1, 2 and 3 available for Robert. For Section 4 we can use old data, just
for the exercise. When the alignment, pop-in fitting and other dress rehearsals
are done, we will take Sections 3 and 4 back to the Magnetic Measurement
Lab to complete the fiducialization, as per Aaron’s plan.
This
Monday’s scheduled laser maintenance was realigned of the oscillator,
again because of degradation of the saturable absorber. Although
this problem last occurred in August, the process is the same. The
high intracavity power slowly causes a decrease in reflectivity of the
saturable absorber, and after large enough loss develops, mode-locking
is affected. The solution
tried in August was to reduce the pump power and compensate with higher
gain in the amplifiers. However,
this appears only to have increased the decay time, and further decreases
in pump power would not only require higher amplifier gain, but also start
to affect mode locking and beam profile.
Periodic realignment works temporarily because the active region
of the saturable absorber is much larger than the mode size, and the beam
can simply be repositioned to an undamaged area.
The new oscillator being built will incorporate a higher damage
threshold saturable absorber and larger mode size for much higher resistance
to this problem. Otherwise the system
operated uninterrupted throughout the rest of the week. Due
to various illnesses and absentees, this weeks workload was not as productive
as anticipated. Most of the time was spent investigating and purchasing
needed equipment for the ATF. New HV power supplies for the rf modulators,
the temperature controller for the I/Q modulator system, additional pop-up
solenoid valves for diagnostics and ion pump “holding” power supplies
for the facility vacuum system. The new quadrupole in beamline #3 was
wired and assigned to the computer system. Marc has re-certified himself
in “Hazardous Waste Generator” training and I have re-certified myself
for “Laser Safety Training”. Mechanically,
Bob has been working with Igor, addressing the needs of the CO2 laser
system. He is also fabricating a phosphor screen for the VISA Experiment.
Missing parts were found relating to the Visa project.
The reorder was canceled and much time and money have been saved.
A large effort was spent assisting our Russian experimenters setting up
their equipment for the BPM experiment in the ATF tunnel. A delay in the
installation of the stripline receivers for the VISA experiment. NSLS
electronic support has been delayed due to conflicting job assignments.
We will begin assembly of two units immediately and are negotiating
the completion of the remaining units with NSLS at the earliest possible
opportunity.
Last Modified: December 3, 2007 |
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