# MEMORANDUM 

**To:** Distribution

**From:** George R. Neil/svb

**Subject:** FEL Upgrade Project Weekly Brief - March 5-9, 2007

**Date:** March 9, 2007

**Highlights:**

This past weekend was dedicated to running the machine at 930 nm for the
ONR funded LIPSS experiment.  The machine ran well and the LIPSS
collaboration took quite a bit of data.  The first three days this week
were dedicated to a shakedown run for a harmonic characterization
experi-ment carried out for the JTO.  During the setup for this run we
again exceeded 2.4% efficiency at 2.8 microns.  We managed to get some
interesting data on the absolute ratio of the second harmonic power to
the fundamental when lasing at the third harmonic and got data on the
relative harmonic amplitudes vs. cavity length and Rayleigh range for
the 3rd through 8th harmonics.  The gun vacuum chamber for the gun test
stand is complete and ready for vacuum firing.

**Management:**

Gwyn Williams gave an invited talk, and Mike Klopf gave a contributed
talk at the American Physical Society meeting in Denver this week.
George Neil represented the FEL group in the Antarctic marathon, placing
14th out of a field of 80 runners.  Congratulations, George!

**Operations:**

Last Friday we set up for a weekend run for the Dark Matter Axion Search
experiment (the LIPSS experiment). We ran the entire weekend delivering
approximately 200 W to the experiment at 935 nm.  On Monday, we
recesiated the gun and switched over to 2.8 micron operation for an
experiment to characterize the harmonic power from the FEL.  This is
being done as a subcontract to SAIC as part of a JTO contract.  The
setup was delayed by a computer glitch that took down our server,
shutting down all control capabilities.  We are still investigating the
cause of this computer system failure.  We recovered the servers on
Tuesday and completed setting up the laser for the SAIC experiment.  The
laser performed quite well, matching earlier performance at this
wavelength with over 1700 W and only 0.63 mA of beam current.  This is
over 2.4% efficiency, well in excess of the modeled performance.  When
we tried measuring the energies in the harmonics we found that the
different harmonic orders could not be cleanly separated.  Several
optical setups were attempted in an effort to cleanly separate the
orders but none were capable of fully separating the higher orders.  We
were able to cleanly separate the fundamental and second harmonic for
the third harmonic lasing and found a ratio of approximately 200:1 as
expected.  We then looked at the intracavity light using a sampling
fiber spectrometer and could get the relative harmonic amplitudes as a
function of cavity length and Rayleigh range.  Detailed calibration will
be required before we can derive the power vs. harmonic number with this
setup.\
Thursday was dedicated to providing beam for making boron nitride
nanotubes in collaboration with NASA Langley.  The machine ran quite
well, delivering over 1 kW to the experiment.  Today we are setting up
for an engineering run for an experiment conducted by Old Dominion
University looking at producing a far off resonance magneto-optical trap
using the FEL.  In parallel we are studying the pointing stability of
the beam in the optical transport.

**WBS 4 (Injector):**

On Monday we re-cesiated the photocathode, which delivered 351 Coulombs
and 107 hours of CW beam time since the last re-cesiation on February
12. D. Bullard continued supporting work for coating the new wiggler
chamber with copper. M. Stutzman and C. Hernandez received revisions
from the editor of Physics Today on their article and worked on those
through the week. The vacuum chamber for the new gun to be installed in
the Gun Test Stand has been completed after the machine shop welded the
end flanges. The chamber is now ready for vacuum firing for reducing
hydrogen wall out-gassing.

**WBS 8 (Instrumentation):**

The ODU folks are ready for an engineering run on their FORT experiment
in User Lab 6.  We have removed the Alignment Mode jumpers from the
Laser Personnel Safety System (LPSS). The jumpers were removed and
certification of the Lab was successful for use with FEL beam. We have
also had a very successful BN nanotube run in lab 1.\
   This week much effort has been spent working on the next revision of
the Embedded BPM Electronics.  Some minor modifications to the schematic
for clarity purposes were performed and good progress was achieved on
the PCB layout.  With the layout becoming more concrete, the dimensions
for the channel RF shields and the processor shield were both
designated.  Both of those designs have been sent out for quotes and
error checks.  These will be ordered once the quotes are received.  The
final dimensions of the electronics enclosure have also been defined. 
These are being incorporated into the documentation and then this will
also go out for quotes and error check.  The bill of materials for this
PCB is being completed.  An order will go out early next week for the
required parts.\
   The 4-Ch RTD PCB was turned over to the fabrication group with the
parts assembly kit.  They are currently progressing with this assembly,
which incorporated the SIPAD technology.  They are also progressing with
the 4-CH Charge Dump/Current Monitor PCB assembly.  Other activities
this week included the assembly of a momentary polarity reversing switch
and the research for the PFIEFFER Vacuum Pump instrumentation.\
   As part of the upgrade to the LPSS system, each user lab is being
outfitted with a PA system to provide warning messages depending on the
changing states of the user lab.  To accomplish this it has been decided
that the 1700 Series Chipcorder sound recording chips produced by
Winbond Electronics will be used to record computer generated warning
messages, and the user lab PLC will be used to trigger the message
playback over the lab PA system. The advantage of using the Chipcorder
sound chips is that they utilize flash memory to store their messages;
therefore power loss to the system, such as a hard reset, will not erase
the pre-recorded messages.  The memory has a 100 year message retention
life and can be over-written 100,000 times.  The 1700 Series chips are
capable of multi-message recording at several different sampling rates
to provide a good compromise between sound quality and memory
utilization.  They also allow for analog input to record computer
generated messages directly to the chip, and provide push-button message
cycling and playback that will be easy to interface the with LPSS. The
RFID tag hardware also arrived from the vendor this week. This will be
used to interlock the correct laser googles with the correct laser
hazard. We were able to setup the I/O and communicate with the RFID
buttons. Some more testing is in order.    Although the ITV1F04A viewer
camera was recently replaced (within 4 weeks), the image being fed from
the viewer was garbled and warranted investigation.  During the access
on Tuesday, the voltage was measured at the camera, and determined that
the 21V being provided to the camera indicated that the voltage
regulator in the viewer control box was bad.  During the next access,
Slim had planned to replace the regulator, but saw that the box
contained an old revision of the control board, so he replaced the
entire board.  The existing camera was fried due to the over voltage, so
the camera was replaced as well, and the viewer was realigned.  The
busted voltage regulator also caused the channel fuse to blow in the
beamviewer chassis, so that was also replaced.\
   Progress has been made this week with the new AMS/Video software. It
was loaded onto iocfel8 this week and tested with the real AMS/Video
switcher hardware. The tests were good and we now are waiting until the
upcoming maintenance period to install the system permanently. We have
also identified the need to upgrade the way the output channels are
selected.\
   A real-time graph of the LPSS status has been created for the
off-site flog reader. In addition to the machine status (beam current,
FEL power, etc.), this allows the user to see where the light is being
delivered through the status of the LPSS. This is just an example of how
the FEL systems data being archived by Devlore can be used to chronicle
the FEL machine and user facility operations and automate the
calculation of up-time and beam delivery statistics.\
   Progress continues in setting-up the two new computer-center managed
servers for production and development of the FEL\'s web-based data
services. We are learning how to migrate from small-scale Microsoft
database back-ends to the more robust Apache/MySQL systems. Special
thanks to the computer center for their prompt involvement in this
activity.\
   FEL shift work and support of FEL OPs this week as well.

**WBS 9 (Beam Transport):**

Improvements and Upgrades

*New Gun Test Stand*

• I worked on the caster on the door for the Power Supply Tank of the
Gun Test Stand.  The new installation height didn't match the caster's
contact with the floor.  Parts were ordered and received.  Neil Wilson
will install the parts next week.

• I continued doing the validation calculations for SF6 tanks for the
New Gun. This week I concentrated on the peculiar flange that mounts the
gun vacuum tank to the SF6 vessel.  I am using formulas from Roark and
Young for this calculation.  The tank calculations are nearly done. We
received a budgetary estimate from Riggins Co. on how much the tanks
should cost.

 •  The JLab Shop finished welding the flanges on the Gun Chamber. The
injector folks are working with the CEBAF Source Lab folks to bake out
the tank under vacuum for 60 hours at 400 °C to diminish the hydrogen
background without softening the flange knife-edges.  

• The gun's resistor assembly drawing package is in a procurement cycle.

• McAllister Technical Services fabrication of the stalk retraction
mechanism is slated for mid March. 

*SF Sextupole Magnet Testing*

• We continued our plan to test the magnets with the power supplies in
Magnet Test with the actual software.  A power supply was been installed
in Magnet Test.  Unfortunately, the communication software to the power
supply is still in development (probably complete next week) and Scott
Higgins can't test out his control algorithms until the development is
complete. 

*Cooled and less resistive Wiggler Chamber*

•  Don Bullard of the Injector Group performed a first attempt at
sputtering the copper coating on the inside of the Test Chamber. 
Unfortunately the sputtering confined itself to just the higher
pressure, bleed-in end of the tube.  Vacuum bursts also made the
sputtering uncontrolled and periodic. We learned we would have to
probably bake the chamber in order to stop the vacuum bursts.  We then
plan to glow-discharge-clean the inside surface. We plan to make the
sputtering more uniform along the length by lowering the vacuum by an
order of magnitude using a magnetic field along the entire length to
ignite the discharge and subsequently define the plasma.  We will obtain
the magnetic field by winding a solenoid coil along the entire length. 
All of this will be tested on the Test Chamber.

•  In a parallel effort, the CEBAF Source Lab Group is cleaning, leak
checking and pre-baking the Actual Chamber #2 and soldering the cooling
tube on the upper and lower edges.  This will ready the chamber for
immediate copper sputtering once the technique is perfected by work with
the Test chamber.

•  Also during our testing, we learned that we need a substantially more
robust copper electrode.  We ordered an 8 ft strip through the JLab
Machine Shop and have machined slots in the end electrodes to accept the
strip. 

Experimental program

*Experiment to see a pseudoscalar particle that couples to photons*  

• The group is evaluating the data from the last Physics run at two
polarizations.  We are also planning to get a new HR mirror (and a
spare) with better reflectivity for harmonics. We also plan to mount the
OC mirror in a cryo mount, anticipating that it can be mounted in the OC
Can that has all four mirrors at cryogenic temperatures. This would make
ready a setup that could run at much higher power before the shutdown.

**WBS 11 (Optics):**

***FEL Mirror Development***

  This week metrology began on the outcoupler for the High Q test.  So
far, it is meeting spec.  This week we did our first measurements of
the ratios of the harmonics to the fundamental, work funded under a JTO
contract to SAIC.  Data was collected not just on the harmonic content
exiting the OC, but also the intracavity contribution.  A proper
deconvolution of the data will have to wait several weeks, until we can
introduce a standard lamp into the FEL optical cavity for calibration
purposes.  We found we had some imaging issues with the exit light, and
are redoing the setup in the lab before reinstalling it on Monday. 
Discussions are underway with a vendor able to produce high purity (\<
0.15%) hafnium dioxide.  We are discussing using it for some of our next
coating runs.

#### Optics General

We started the week setting up the diagnostic hutch to accommodate the
FEL harmonic content measurement experiment. This hutch is located
immediately after the output coupler cavity mirror. Taking advantage of
the Friday program change to 1.06um we have been aligning a new setup in
Lab 4. We hope to take 1um beam between ODU runs to monitor beam
pointing stability and mode size. This will be done first in alignment
mode and then in CW to compare the difference in beam between the two
states.

* **Optic Student Activities***

Activities this week mainly were centered on fixing/analyzing the
various components on the Optic Group's pump carts. These three carts
were troubleshot and are now in good working condition. The two carts
with turbo pump systems are in the mid 10\^-8\'s and are now labeled
OPC01 and OPC02. (Optics pump cart 1 and 2) Both have been purged
several times with nitrogen and seem to be in great working order. The
only thing that needs to be checked out on OPC02 is the cold cathode
gauge. It was steadily reading consistently with OPC01 until late
Thursday and then started giving very false readings. The third, OPC03,
is the Pfeiffer Turbo Cube and is also in the mid 10\^-8\'s despite
having a small leak in the nitrogen purging system that will, hopefully,
be fixed by the close of business today.

 

The various Residual Gas Analyzers (RGAs) on these pump carts were also
troubleshot this week. A spreadsheet that was created shows the various
locations and status of the RGAs we have in Lab 2. Two Electronic
Control Units (ECUs) were determined to be faulty along with two
filament assemblies. Stanford will be called today and contacted about
fixing these units.

 

Assistance was also given to Dave Hardy in the form of construction and
fabrication of an Optical Beam Position Monitor (OPBM) chassis and its
components so Dave can begin wiring the chassis as needed. A setup
downstairs was also constructed for Michelle Shinn to measure the
intensity of the various harmonics that the FEL produces.

#### Lasers and diagnostics

We helped with the JTO study by setting up and aligning the diagnostics
in the FEL vault. This week the significant time was spent assisting our
ODU Users in preparation for their Friday experiment. We helped to
certify Lab 6 on Thursday and Friday, and then set up the Lab FEL beam
delivery and monitoring system. One of the Ti:Sapphire lasers for EO
sampling is now back up and running at specification after a systematic
optimization. A report about the FEL diagnostics is under preparation
and a paper about laser beam shaping is near completion.  The Antares
drive laser is operating to specification.

**Terahertz:**

This week we presented details of our THz user facility and some of our
imaging data at the March meeting of the American Physical Society in
Denver.  We also worked on the safety documents in preparation for a Hx
run by Harvey Rutt next week.

**Users:**

The LIPSS collaboration would like to thank the FEL Team for an
outstanding effort as we conducted a 5-day Physics Run using mid-900 nm
FEL beam, very near its short wavelength limit. FEL Operations for this
"round-the-clock" effort was three shifts per day with one FEL operator
per shift. This level of intense operations had never been done before
on this FEL. The LIPSS team had two members on each shift collecting
data and maintaining the stability of the FEL light into the LIPSS
setup. Although the setup was designed for steady FEL power levels,
instability in the FEL Optical Cavity (probably due to drift caused by
absorption in the HR from the 3^rd^ harmonic which is in the UV), caused
the power to fluctuate into the LIPSS setup and was considerably less
than nominal levels available to typical users. Nonetheless, over two
dozen two-hour sets of runs were accumulated and analysis of these
images is underway. Again, many thanks to the FEL Team from the LIPSS
collaboration.