# MEMORANDUM 

**To:** Distribution

**From:** George R. Neil

**Subject:** FEL Upgrade Project Weekly Brief -- October 29-November 2,
2007

**Date:** November 2, 2007

**Highlights:**

The Gun Test Stand HVPS is under pressure in preparation for its first
HV test next week. The GTS diagnostic beamline has been prepared for its
vacuum baking which will commence today. We delivered to our THz lab a
16 Tesla solenoid magnet to be used in materials studies (it will also
be useful in discovering the effect of stray fields on the FEL linac
operation 4 meters below!). We have also been doing a lot of
preventative maintenance on the FEL hardware in preparation for bringing
beam up again in late December.

**Management:**

We have been doing the final approval sign offs of the budget packages
funded under the first increment of ONR funding which arrived last week.

 

We met to solidify our approval and test readiness procedures required
for full operation of the Gun Test Stand. That appears on track and the
required documentation and signoffs have been identified.

 

We have also been coordinating our running plans for the year with the
rest of the lab. It appears that we will be able to operate throughout
the year except for June and the first two weeks of July due to a
shutdown for cryo refrigerator work.

Gwyn Williams met at LSU to discuss future light source development
collaborations.

**Injector:**

The GTS beam line was prepared for vacuum bake during the week after the
Vacuum Group installed a much needed Residual Gas Analyzer. The bake was
started early today. The old IR Demo gun vacuum chamber that served as
temporary chamber for the GTS gun electrodes was sealed off with
blank-off flanges and transported to the machine shop. This chamber will
be pumped down and bolted to the new SF6 tank for the pressure testing
scheduled for next week. We held a GTS progress meeting on Tuesday where
the Safety Systems Group reported that PLc\'s have been powered up this
week as part of initial testing and system troubleshooting.

We started collaborating with Philippe Piot\'s group at NIU on injector
modeling by sending him field maps of solenoids and cavities.

D. Bullard finished polishing the FEL gun electrodes which are ready for
cleaning early next week . He also helped re-building the high pressure
rinser used for cleaning the SRF cavities. This time the gun electrodes
will undergo high pressure rinsing after the usual wet chemical
cleaning. Most of the internal FEL gun parts are being wet cleaned for
UHV conditions by the Vacuum Group in preparation for assembly next
week.

The buncher cavity has been prepared for baking the injector beam line.

**RF**

RF Zones 3 & 4 were acid cleaned and flushed this week.  The LCW flow
improved for each zone from 32 & 35 gpm respectively to 65 gpm.  Zone 2,
the Buncher and the Quarter will be treated next week.  The various
vendors will be contacted to determine their equipment can withstand the
acid cleaning.  The Buncher cavity was prepared this week for a beam
line bake to clean-up the vacuum after the SF6 Gun leak.

 

**GTS HVPS**

The SF6 system for the GTS is nearly finished.  It is being cleaned of
moisture and dust.  The SOP to safe and operate the GTS HVPS will be
started next week.

**Instrumentation and Controls:**

The major efforts continue to be the Gun Test Stand and completing the
Lab 5 LPSS. At the beginning of this week we successfully managed to
generate 100 ns pulses with resolutions better than 1 ns.  These high
precision signals were generated using a DG-535 which is a commercial
pulse generator.  The interface to this device was installed, checked
out, and verified to work properly.  These two signals are used to
trigger the first Pockel Cell of the Drive Laser regenerative amplifier.
 After this was tested with the actual hardware and verified to work
properly we discovered that we would in fact need to generate two more
channels to trigger the second Pockel Cell.  To better utilize the
instruments that we have available we decided to remove the DG-535 used
for triggering the WESCAM and replace that with a fixed delay Timer
Card.  This second DG-535 is now placed in the GTS control racks and
once the software is ready to control this we will begin configuring the
two channel outputs.  The fixed delay Timer Card is currently being
configured to generate the proper delay signals.  The timing parameters
have all been configured and tested. We are continuing with the
configuration settings to trigger on both rising and falling edges. Once
this is completed we will install this card to provide both the timing
signals for the WESCAM as well as other camera synchronization.

    The SF6 system is in its final shakedown. There were 2 very minor
leaks that required finding a bigger wrench\... The system is being
dried out using the instrument air. SF6 gas will be filled next week to
allow for HVPS testing. The SF6 panel meter was configured and tested
successfully.  The difficult menus of the OMEGA meter managed to make
this a more complicated task than originally expected.  Once the
navigation between these menus became easier the settings were all
configured to read the pressure transducer readback from 30 inHg to 15
psi.  This was tested and verified to work properly.

   Other work includes looking into the M55/56 chassis and preparing
for the FEL injector bake. There has also been progress on the LPSS
master software.

**Electron Beam Transport:**

Improvements and Upgrades

*Gun Test Stand (GTS*)

• In building the SF6 Gun Tank system, the JLab Shop welded flanges and
ground smooth the inside of the Outer Conductor Adaptor (the spool
leading to the High Voltage Power Supply Tank).

• The test of the House Air Line to the SF6 system was completed on
Tuesday morning and the line is commissioned.

• Matt Marchlik continues work on the hutch for the drive laser.

*SF Sextupole Magnet Testing*

• Magnet Test advanced to the third magnet on the test stand.

**High Power Optics Risk Reduction**

  In last week's report I wrote that the analyses required to extract
absorptive loss from the thermographic data was complicated by
conduction from the sample to the aluminum mirror holder.  While I had a
plan for an insulating holder, Joe Gubeli had a more elegant idea.  He
quickly drew it up and I received the part from our machine shop
yesterday.  I have just started preliminary testing, and find that I
need to reposition the IR camera and make a couple of other changes to
get good data.  I'd also like to add the ability to irradiate the mode
area with UV light to see how this influences the loss at the IR.  To
that end, I calculated the amount of power available from a high power
Xe arc lamp, and it appears to be sufficient.  I am setting up a test to
see if I can image the source to a small enough area to be useful, and
get the UV power required.

**Optics**

The optical transport is now seeing its lowest vacuum level of 1e-7
torr. The addition of those ion pumps last week not only brought the
vacuum level down but, more importantly, it allows us to have a very
quick pump down. If we have to in work in the transport we can have the
system operational after repairs in a matter of days instead of the
typical one week Given the difficulty in installing Turning Mirror
Cassette (TMC) 1 it was decided to move to install TMC 4. The
installation of TMC 1 would require the repositioning of mirrors cans 2
and 3. In addition the location of TMC 1 will change when the upgrade
collimator is installed. TMC 4 (the first turning mirror assembly
upstairs) should be able to "drop" in place without shifting the other
mirror assemblies. We are preparing a quote to replace the mirrors in
the transport with dielectrically mirrors centered at 1.6um. This should
allow us to send a larger fraction of 1.6um light upstairs. The output
coupler mirrors and frames that should have been sputtered and brazed
this week have, unfortunately, been delayed again. The ion gun in the
sputter chamber is sputtering some unknown metal on some test samples.
Tests are underway to determine the metal species as well as the
mechanism for this sputtering. Neither the optics nor the frames will
get gold sputtered until this is rectified. We have received the
mechanical drawing for the existing 'collimator-lite'. We are designing
a shield to prevent the first of the three optics in this vessel from
absorbing stray light.

 

**Lasers and Optical Diagnostics:**

The measurement on the second harmonic pulses for the Antares laser
shows over fifty percent conversion efficiency with individual pulse
energy up to five hundred micro-Joule. We also measured the pulse
duration which appears to be about fifty picoseconds. The
characterization on the spatial phase was not complete due to the
failure of a diagnostic instrument and will be done once it is fixed.
Testing of the DLPC shows good improvement over last week. We are
putting much more effort on the diagnostics needed for running the laser
and injector. The laser for the cathode scanner has been received and we
will start to set it up next week with other collimating optics near
beamline. We are now making preparations for moving the whole laser
system into the GTS site.

**Terahertz:**

This week, work continued on the magneto-optical experiments on the U4IR
beamline at the NSLS. We unfortunately discovered some problems in the
data. One issue is the lack of repeatability from the previous runs in
August. That problem may be due to an adjustment made to the steering of
the beam into the spectrometer. We were unaware that the steering had
been changed to optimize the throughput in the mid IR shortly before our
run began. It appears that we will still be able to use data collected
in the current configuration, but the lack of repeatability may limit
our ability to publish the data. In any case, we are continuing to take
measurements and accomplish as much as possible. The other problem we
have seen in the data is more troubling. We see a fairly significant
variation in the spectrum at different locations on the sample. The
cause of this is not yet clear, but we are investigating this now.
Hopefully we can resolve this problem before our run ends this weekend.

Though both Michael Klopf and Gwyn Williams have been away on travel for
most or all of this week, headway continued to prepare the 16 T magnet
for installation in Lab 3 and for the acceptance test scheduled the week
of 11/12/2007. Neil Wilson and his group did a fantastic job of
preparing the documentation and scheduling to get the magnet craned up
to the 2^nd^ floor of the FEL on Wednesday. They placed the magnet on a
heavy duty dolly and it can now be moved into location when ready. Other
preparations regarding ODH hazard analysis are continuing and we are on
schedule for the acceptance testing.

Finally, as an addendum to the THz report from last week, we had a
meeting at AES on 10/22/07 with Alan Todd and Hans Bluem to review
progress on the compact THz source, discuss debriefings from several
SBIR proposals, and begin developing a testing plan for characterizing
the output of the compact source.

**Word version:** [FEL Upgrade Project Weekly Brief -- October
29-November 2,
2007](http://www.jlab.org/accel/fel/documentation/07weeklybriefs/upgradeweek07oct29-nov2.doc)