# MEMORANDUM 

**To:** Distribution

**From:** F. Dylla/grn

**Subject:** FEL Upgrade Project Weekly Brief - September 25-29, 2006

**Date:** September 29, 2006

**Highlights:**

We have an exciting milestone to report in this week's edition: the
first lasing on the cryomirror assembly that we installed into the FEL
outcoupler assembly two weeks ago. We have lased at 1.6 microns at cw
powers at the kilowatt level using this new mirror, and significantly we
observe no absorbed power, change in optical figure, nor vacuum activity
with this laser power loading. The accelerator match into the wiggler
region is far from optimized nor have other parameters been optimized
with this new configuration, however we are very pleased with the
initial performance. To remind our readers, we have proposed and
bench-tested cryo-cooled (to approx. 50k) sapphire mirrors for high
power FELs for several years. By cooling sapphire to this temperature
the power handling capability is theoretically improved by over two
orders of magnitude due to significant (\>10x) enhancements in thermal
conductivity and significant decrements (\>10x) in thermal expansion.
However, the real test of this concept is the actual performance of an
optical cavity mirror in an FEL. A number of real world environmental
factors (coolant induced vibration, laser desorption of cryosorbed
gases, color center formation in cooled substrates) could have foiled
the test. So far so good. As noted in the detailed operations report
below, we have optimization work to be completed before we incrementally
push up the current and test the mirror performance at higher powers.

***Other accomplishments this week include:***

\- the first direct measurements of the injector emittance with our
improved injector diagnostics-which show that we do not have transverse
emittance growth from the injector to the wiggler.

\- the completion of construction of our second photogun assembly. This
assembly will be moved over to the new FEL Injector Test Stand area next
week for vacuum tests. This gun assembly will be used to test photogun
and injector hardware and will serve as a needed back-up to the primary
photogun in the FEL.

**Note**: please hold these dates as the tentative dates for the annual
review of the Jefferson Lab FEL program; Jan. 17-19, 2007

**Special Note**: We reprint this note from the ONR Website:

On August 24, at its 28th Annual National Training Conference in New
York City, Blacks in Government awarded its 2006 Meritorious Service
Awards. Among the recipients was ONR's Quentin Saulter, program manager
for directed energy technology (Code 351), for his work with the Navy's
free-electron laser program and other directed energy projects from 2004
to 2006 as well as for his leadership of ONR's Future Engineering
Faculty Fellowship Program and his work with historically black colleges
and universities

On behalf of all of Quentin's friends and colleagues at Jefferson Lab,
we congratulate him on this important award and recognition of his
accomplishments for ONR. We also wish Quentin well on his next venture
which we all hope involves continued interaction. Quentin left ONR last
week to join the Directed Energy program at the Air Force Research
Laboratory at Kirtland AFB in Albuquerque.

**Management**:

We are pleased to announce that the FEL program at Jefferson Lab moves
from Department to Division status within Jefferson Lab as we start the
new fiscal year on Monday. The FEL program will continue to maintain
strong ties to the Accelerator Division as we proceed with the new
visibility that this elevated status presents to our stakeholders.

We worked with ONR to schedule a monthly status meeting at ONR
(tentatively during the week of Oct. 16^th^ ) and our annual review
dates (Jan. 17-19,2007).

We held our monthly coordinating meeting today with our collaborators in
the Biomedical Photonics Consortium. Earlier in the week we received
reviews on our

pre-application to the NIH Interdisciplinary Research Center proposal
program. The pre-application garnered excellent reviews on the proposed
science but needed examples of consortium results before meeting the
threshold for a full application. The coordinating team has proposed a
path forward which will generate near term results prior to the next
application deadline in 2007.

Michael Kelley has received a grant from DoE to support a doctoral
student at William & Mary and one at Virginia Tech, working on
improvements to niobium processing for SRF accelerator technology, the
heart of the FEL.

**Operations:**

By Friday of last week we were finally far enough along in hot checkout
to turn on the beam.  All the cables in the injector had been modified
so we had to start from scratch to find phases close enough to get beam
out of the injector.  This went fairly smoothly and we were able to get
beam out of the injector, through the linac, and around the machine to
the energy recovery dump.  The energy from the linac was low and the
match was not very good but we had something to start with for injector
setup.\
On Monday we started with a careful full injector setup.  This was
slowed significantly with a vacuum problem.  We kept getting vacuum
trips in the injector.  Checks of the vacuum pumps indicated that the
trips were spurious, i.e. there was no real vacuum rise that initiated
the trips.  In parallel with the injector setup we tried to debug this
problem. 

By the end of the day we had run our injector setup script but we were
not sure of the results due to spurious trips during the script.  We
continued with this on Tuesday and completed the injector setup.  Once
it was properly set up we tried out the injector multi-slit with the
triggered camera.  We were finally able to measure the vertical
emittance and Twiss parameters in the injector.  Interlacing in the
camera prevented this in previous attempts.  The emittance measured in
both axes was approximately 8 mm-mrad.  This is essentially the same as
what we measure in the wiggler region, indicating that the transverse
emittance does not grow from the injector to the wiggler.  We then
roughly phased the linac and found that we had to find the gradient
limits in zone 3 again since we had re-calibrated this zone and the
gradients had changed.  While we were doing this we finally found the
problem with the vacuum crate and put in a temporary fix.  Once we had
recovered the linac gradient we measured the longitudinal properties and
found that the bunch length was the same as it has been recently and
that the M55 traces looked good.  The match and steering was still
pretty bad.  To cap off the day we took data on the 3F and 4F viewer
sensitivity and re-tuned the zones to reduce window heating.\
  On Wednesday we explored the steering and dispersion in the system. 
We found a large vertical dispersion in the wiggler that was not present
in the 3F region.  This implied that the dispersion was coming from the
optical chicane magnets.  These magnets should have no vertical
dispersion unless the orbit is very bad.  We did find that a large
vertical kick at the entrance of the chicane could eliminate the
vertical dispersion in the wiggler.  This all implies a bad magnet in
the optical chicane.  We decided to try lasing anyway so that we could
start on the setup of the beamline after the wiggler.  We obtained
lasing at 1.6 microns and tuned the wavelength from 1.56 to 1.64
microns.  The maximum power was at 1.6 microns as expected.  While
operating with 6% duty cycle and low power we found no vacuum activity
or temperature rise in the cryomirror.  When we changed the wavelength
there was a brief rise in temperature that eventually went away.  We do
not know what causes this.  The laser efficiency seemed low, though it
was hard to tell since the power was so low.\
 On Thursday we worked on improving the match around the machine.  We
found a match that increased the Happek signal, despite only shortening
the pulse length a little bit.  The energy spread induced by CSR was
also less.  We did a BLM walk and found losses low everywhere except for
5F10.  Using the new halo monitor we were able to prove that the loss
evident on this viewer came from some other point in the accelerator.
Finally we started ramping up the duty cycle while lasing and studied
the performance of the cryomirror at moderate power.  We found that the
efficiency was indeed low.  It could be improved a bit by reducing the
Rayleigh range but was still lower then typical.  We ran the power up to
900 W.  We found that the mode, as indicated by the coherent harmonic
light pattern, was not changed when the laser was changed from pulsed
lasing to lasing at over 500W.  We did find that the output coupler did
steer more than we would like. We are attempting to find the cause of
this.  We found that the new match did lase better than the previous one
but still seemed lower that we have seen in the past.  We are trying
today to improve the match to get the gain and efficiency up.

**User News:**

Many of us heard user Rox Anderson from Harvards's Wellman Laboratory of
Photomedicine on NPR this week talking about laser removal of tattoos
and specifically a new laser degradable ink.
<http://www.npr.org/templates/story/story.php?storyId=6126963&sc=emaf>\
\
We also heard from user Mike Smith from NASA-Langley that carbon
nanotubes synthesized at the JLab FEL have been selected as one of the
materials to be tested on the International Space Station on
MISSE-6(Materials on the International Space Station Experiment-Mission
6).  MISSE missions test new materials for space exploration, allowing
long duration exposure in earth orbit.   Polymer panels reinforced with
CNT\'s synthesized at JLab are slated to launch to the ISS aboard the
space shuttle in December of \'07.\
\
Gwyn Williams visited the THz group of Jim Kolodzey at the University of
Delaware this week to give a seminar and to discuss user experiments.

This week Mike Klopf and Gwyn Williams had a meeting with Gunter
Luepke\'s group at William and Mary, see the THz news for more details.

**WBS 4 (Injector):**

The photocathode gun is operational, it delivered 6 Coulombs during the
week for FEL ops. High voltage testing of the field emission suppression
coating continued this week. The tests show current below 6 pA at 32
MV/m and 125 kV, much better that any previous tested coatings. Drawings
for a new corona shield that will incorporate a series of rods for doing
cathode re-cesiations without opening the SF6 gun tank were signed off.\
\
We achieved an important milestone by completing the gun assembly for
the Gun Test Stand this week. As can be seen in the picture below, the
gun electrodes are coated with the field emission suppression film.

![](media/image1.jpeg){width="2.5388888888888888in"
height="2.9881944444444444in"}

**WBS 8 (Instrumentation):**

A full injector setup was done this week.  With the help of S. Benson
and C. Hernandez the injector phasing procedure was refined.  The
corrections and clarifications are currently being made.  The Injector
Phasing Script manual was updated with minor changes and will be posted
in the FEL procedures book along with the updated injector setup
procedure.\
    Work was done with K. Beard for setting up some data acquisition for
the LIPSS experiment.  Testing was done to define the hardware needed to
properly run the camera without drop outs as well as the memory storage
needed for recorded video.\
    Operational software improvements are being worked-out regarding the
drive laser pulse controller (DLPC) to accommodate the new use of the
DLPC \"Pre-Trigger Delay\" in the viewer camera timing system. In order
to achieve \"transparent\" performance (i.e. changing appropriately and
automatically without the FEL operator\'s attention) we will be using
the video switcher system to provide the system with proper context
information to know how it should be configured. This is due to the fact
that the sole-motivation for the camera pre-trigger is for the emittance
measurement frame-grabber system using monitor #17 from the video
system. The operational need for the camera pre-trigger is linked to
using the video system with the frame-grabber.\
    Having previously improved the epics2devlore data exchange software,
we were able to easily begin archiving the FEL User Lab usage and status
of many of the key EPICS variables associated with the LPSS. This will
allow us to automate the tracking of how the FEL light is delivered to
users.\
    We worked on the embedded IOC design for the FPGA memory block. This
allows use of the ColdFire bus bridge to access the memory with reading
and writing. Integration of the ADC board general purpose board and
ColdFire boards continues. The design process of the 3U General Purpose
I/O Card has been completed.  The layout of the prototype board has been
finished and several prototypes have been ordered for testing and
verification.  The parts list for this project has been generated and
the parts needed to assemble the prototypes have been ordered.  The
front panel design for this card has been completed. This panel along
with the front panel for the Beam Viewer Control Cards and rear panel
for the crate were all ordered.  The first revision of the Beam Viewer
Control Card has arrived and is currently being assembled.  The
remaining parts that were ordered for that project have all arrived and
placed with the parts kit. \
    Install and wiring of Lab 5 LPSS continued. Support was also given
to the Optics group for various efforts. We also assisted with getting
the advanced drive laser in User Lab 6 operational and ready for a LPSS
certification.  Power was connected and checked out along with
installing the LPSS interlocks.

**WBS 9 (Beam Transport):**

#### IR Machine Operations

• In work for the New Gun and Injector Test Stand, McAllister Technical
Services continues design of our stalk retraction system. They plan to
start asking about clarifications to our specification in about 1 week.
Procurement issued a contract to Riggins Co. to bring the tank for the
high Voltage Power Supply back to operable condition culminating in a
"hydro" test. They will call for delivery of the tank to their facility
when they are ready. Cleaning the gun chamber is planned for next week
to ready the chamber for the vacuum bake-out. Howmet Company, a local
manufacturer is still working on a ball park price for heat treatment in
their vacuum furnace.

• Concerning work on the second wiggler chamber, the shop removed the
last two kinks near the ends and completed the welding of the
strong-back at the BPM flanges. We now plan to solder cooling tube to
the chamber and finally add the copper flash to the inner bore.

• With regard to the short-term plan to keep the downstream OCMM from
moving due to the heating and expansion of the Wiggler Chamber, we are
making a new anchor piece for the downstream chamber.

• With regard to SF sextupole, the shop is making longer, more easily
removed pins to substitute for the pins at the two yoke separation
surfaces. One made, Neil Wilson's installation crew can perform a
disassembly and reassembly in Magnet Test to mimic the vault's cramped
conditions. Then Magnet Test will be able to do their repeatability
test.

• Facilities Management continues working on raising the capacity of
that Drive Laser Room's cooling unit.

***Experimental program***

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

• I am designing the parts to hold the new pole tips in the proper
location and restrain the Purcell gap pole sheet in the GW dipoles.

**WBS 11 (Optics):**

#### FEL mirrors

I attended a kickoff meeting of the ONR-funded Optics Improvement
Collaboration in

Ft. Collins, CO.  Also in attendance were Henry Freund (SAIC) and Albert
Ogloza (NAWC, China Lake).  I also attended the 38th Annual Symposium on
Laser Damage in Boulder, CO.  While there I learned about some exciting
developments in high damage threshold coatings and absorption levels at
various wavelengths.  Our talk on our cavity optics was very
well-received, based on the many favorable comments.  Several
manufacturers of commercial optics approached me about using the FEL as
a source to evaluate their products.  I also met with current and
prospective vendors of our cavity and transport optics and windows.

***Other Activities:***

This week, I am happy to announce, we have lased on the 1.6um
Cryo-cooled mirror. To my knowledge this is the first time a cryo-cold
mirror has been used as a cavity mirror. We started the process slowly
to condition the optic. We allowed THz radiation from the dipole magnet
to fall on the optic. We saw neither a change in the diode temperature
nor a change in the vacuum. We started lasing at low duty cycle and
ramped up to CW at 1mA getting 1kW of power on the power meter. We saw a
slight rise in the mirror temperature of a few degrees when running at
higher power. Because the rise can be seen on both the inlet and outlet,
we suspect that the rise is due to scattered light. It also appears the
OC mirror steers in pitch when ramping up the power but does stabilize
after a short period.

We are preparing four OC cavity mirrors for brazing. One is a 1.6um R90%
in a cryo-cooled frame. This mirror will be a backup to installed R80%
mirror if we need a little more efficiency. The others will be brazed in
room temperature mounts for wavelengths of: 1.2um, 1.6um R90% and 1.6um
R80%. We are also in the process of designing the much needed cases to
store both un-mounted and mounted OC mirrors.

We have moved and certified the Advanced Drive Laser for use in Lab 6.
This was done to allow us to turn the laser on regardless of the machine
state of the FEL. Characterization of this laser should progress quickly
now. The Drive Laser EO cell #2 was replaced this week. This replacement
increases the cell throughput by a factor of four. The electronics for a
resonator circuit at 37.425MHz is in progress. The circuit will be used
on the Drive Laser EO cells to improve its performance. Work also
continued on building a photodiode to measure the relative phase shift
of the Drive Laser.

Drawings for four additional mirror cassettes and their related
equipment were submitted to the machine shop for fabrication. We will
add low power lab transport hardware in Labs 3 and 6. Labs 3a and 5 will
receive high power equipment. This, when complete, will populate all of
the user labs with optical transport hardware.

**Terahertz:**

On Monday, I presented a seminar for Gunter Luepke's research group at
William & Mary to describe the JLab-FEL THz research program as well as
the details of some of my previous research on nonequilibrium phenomena
using the pump-probe technique. Gunter directs a very active and
motivated research group that has recently expanded their lab spaces as
well as the number of graduate students in the group. Following my
seminar, Gwyn and I were able to discuss our THz research program in
more detail with them. One of our planned experimental setups is to
build a THz pump-probe system which is of particular interest to
Gunter's research group. There are numerous research possibilities for
THz probing of nonequilibrium dynamics and we are working to build
collaborations with other scientists in this field.

As we returned to beam operations this week, we have recertified the THz
lab and are looking to perform some THz transmission measurements if
possible by the close of business today. Also, we received our repaired
Pyrocam this week and hope to perform tests with beam today to verify
proper operation.