# MEMORANDUM 

**To:** Distribution

**From:** F. Dylla/grn

**Subject:** FEL Upgrade Project Weekly Brief - July 3-7 2006

**Date:** July 7, 2006

**Highlights:**

With a week shortened by the July 4th holiday and a required cryogenic
electrical switchover on Wednesday we used much of the available
time for needed maintenance activities that had been on hold: cleaning
up the vault, fixing a leak at the beam dump, and readjusting and
calibrating viewers.  We also installed some THz absorbers and finished
the installation of the helium feed to the output coupler can for the
cryogenic mirror test in a couple of months.  On Thursday we did a
careful set up and rephasing of the machine in preparation for our
continuing studies of efficiency.  On Friday we re-established high
lasing efficiency and performed further studies on the optics.

**Management**

On Friday we hosted a tour for RDML (sel) Nevin Carr and discussed
scaling options and timelines for high power FEL development.

 

We also prepared for the JLab Science and Technology Review on 7/12-13. 
Fred Dylla, Gwyn Williams, and George Neil will be giving presentations
to the DOE committee on the FEL program science activities. 

Gwyn Williams presented an invited talk at a meeting organized by the
4GLS group at Daresbury Lab.  The meeting, \"New Scientific
Possibilities with High Power THz Sources\", was attended by 70 people,
over 50 of whom are new to the field and come with many innovative
ideas.  Our sister labs, Brookhaven and the UCSB FEL, as well as Yale
and RPI also gave presentations.  There was much interest and off-line
discussion of experiments at our facility.\
\
This week our REU students gave their mid-term presentations to their
colleagues.

This week we hosted a visit by the students of the NSF-sponsored
\"Research Experience for Undergraduates\" program from William & Mary. 
W&M REU students Raul Birceno, Megan Ivory and Elizabeth Scherrer are
working here this summer under the direction of Carlos Hernandez, Gwyn
Williams and Michael Kelley, respectively.

**Operations:**\
Further analysis of the mirror temperature profiles displayed last week
suggests that much of the sharpness of the temperature peak observed can
be attributed to three-dimensional effects in the cooling of the
surface.  We will continue our analysis and measurements to quantify the
effects and impact on lasing.

**WBS 4 (Injector):**

The photocathode has delivered 76 Coulombs and 40 hours of beam time
since the last re-cesiation on June 26. The NEG sputtering test chamber
was baked to 220C for 11 days but a minor leak in the NEG wire support
rod opened up. We are fixing the leak before preparing for connecting
the power supplies for depositing the NEG coating. We continued to work
on the Injector Test Stand layout and produced 3D models for positioning
the resistor transmission line connecting the HVPS and the gun.

**WBS 8 (Instrumentation):**

The primary goal of the shutdown days earlier this week was to clean up
the FEL vault and eliminate potential trip hazards and other clutter. 
We also spent some time straightening up the control room patch panels
and cable connections that exist there.  Several temporary cables were
removed and permanent installations were their replacements to free up
patch panels and to improve overall system integrity.  We also took
advantage of the FEL vault opening to perform some approved maintenance
and installations.  One of the specific tasks was the installation
of some RTDs on the new THz traps.  A RTD was placed on each of the
traps and all four were connected to a control chassis and can be viewed
via our video system.  This is a first order experiment to help us
identify the effectiveness of these devices removing the THz.  Other
work in the vault included the installation of Synchrotron light monitor
assemblies with ND filters in the 4F05, 4F08, and 4F12 regions.  The
1G01 viewer was replaced with the new bellows and the electronics were
all reinstalled.  The camera was replaced with a new one that wasn\'t
damaged by radiation and the viewer was then focused and aligned.  The
Happek insertable lens assembly cover was modified to eliminate some
scrapping and then reinstalled.  We also aided a user from Maryland
University with the alignment of camera and system checkout.  The
OTRI interferometer for this experiment is now in place, has lamp rings
wired to the 2G viewer, and is ready for operations.  The associated
video and stepper motor cables were hooked into EPICS so controls and
readbacks are now available.

    Further work has been spent on the LPSS this week.  An Ethernet
module was added to the new LPSS PLC in Lab 4.  The PLC was configured
to properly handle the Ethernet and Controller Link modules.  It is now
communicating with an EPICS application.  The stepper motor program has
been installed on the Lab 4 LPSS and should be tested by end of business
today.  The limit switches and controls have been tested successfully
back the PLC and EPICS readbacks. We have moved forward in connecting
more of the Lab 4 LPSS to the Master LPSS.  We continue to make progress
in upgrading the \'FEL User Lab LPSS status interface boxes\'. The
AutoCAD drawings for the boxes and for the wiring diagrams are being
worked on, the mechanicals are completed and need to be signed off while
the wiring is making forward progress.  An overview of how the system is
to be used by the users has written.  On other fronts, another video
crosspoint switcher has been readied and provided for User Lab 4 for the
Aerospace systems and we are working on the 10MHz timing distribution
system.  The problems with server stability on laser.jlab.org have been
solved and new tools to do bulk processing of the devlore database have
been written.  A Mirror Cassette test fixture was constructed to allow
us to troubleshoot the lab stepper motor system for the mirror
cassettes.  We also assisted with the electronics work to repair the
Mode Locker as a couple of components failed on the PCB and these were
identified and then replaced.

    The PCB order for the Single Board IOC Module was completed this
week and the board is currently in manufacturing.  A parts kit is being
assembled with the in stock parts and as others arrive they are being
added.  A development plan for how to bring the board online piecewise
has been developed.  Further development of the application code for the
Cyclone II is ongoing as we prepare to bring the prototype online in the
next couple of weeks.  Since the production of the Single Board IOC has
been delayed so long we are trying to use the two development boards for
the FPGA and Coldfire to test the bridge with actual hardware.  This is
moving on and should help expedite the process of bringing online the
prototype.  We are also nearing completion of the 12-Slot Digital I/O
Crate Backplane.  This backplane will be suitable for digitally
controlled systems such as the Beam Viewers, Valves, etc.  The crate is
intended to incorporate the General Purpose I/O Module with a Single
Board IOC for an EPICS interface.

    More components have been added to the ITS Vault 3D model that will
further define the limits of motion of the components that will be
inside the vault.  This will help us to better plan the installation
effort.  A redesign of a compact blocking flag has begun, this will run
off of an electric motor rather than a solenoid and can be operated
through remote controls.

**WBS 11 (Optics):**

#### FEL mirrors

From a operations point of view, this has been a slow week.  But we are
reaping benefits from the analysis of the thermographic data taken last
week.  Using FEA software, we were able to approximately reproduce the
thermographic profile with reasonable laser beam parameters and absorbed
power - if it is all absorbed on the surface of the mirror.  An open
question is whether the absorption is in the coating or in the
substrate.  We are leaning towards the former - but this implies a
higher than anticipated level of absorption in the coating.  Causes for
this absorption, and ways to test these hypotheses are under discussion.

As an addendum to last week\'s report (and thus refuting one
hypothesis), we do see the thermal spike at lower currents (as low as
0.4 mA and 650 W).  The spike also tracks the laser mode as we steer it
about the OC mirror. 

The three silicon substrates that were especially selected for coating
with 100 nm of aluminum, and then a modified \"harmonic control\"
coating for 1.6 microns were shipped to the vendor late last week.  We
anticipate receipt in several weeks.

We also welcome the return of Ms. Alice Ohlson, now an undergraduate at
MIT, to the team.  Ms. Ohlson will be assisting in a systematic study of
the damage threshold of mirrors produced under our optics improvement
program.

***Other Activities:***

With most of the group taking advantage of the Tuesday holiday by also
taking Monday as a vacation day, we had a short week. To confirm the
lack of sensitivity of the IR camera looking at the FEL HR cavity
mirror, it was taken out and spectrally scanned with a spectrometer. The
result showed a much reduced sensitivity at 1.6um than at shorter
wavelengths. The visible filter in front of the camera also contributed
to this sensitivity drop. We installed a temporary IR camera while we
work on the original. Received another on-loan EO cell from the vender
and tested it on the drive laser with a resulting good beam mode. This
solved the previous suspicion that the first EO cell was defective. A
subtle issue with a slightly expanded beam still needs to be rectified.
Work on the advanced drive laser continues. A magnetic shield was
installed at the place where EO cell will be inserted. The whole system
is ready and waiting for recertification. A faulty RF amplifier and
power supply to the Drive Laser's mode locker was replaced. The Drive
Laser is now performing according to specifications. A design to install
a 440l/s ion pump directly to Lab 2's Mirror Cassette was worked on. We
plan on installation of this pump on the 14^th^. Progress was made on
cryo-cooling the OC cavity mirror. The transfer supply line to the OC
vacuum vessel was successfully leak checked and is ready for a final
connection. Three sets of OC frames were received from the machine shop
and are in the queue for brazing. These will be used to test our mirror
to frame brazing techniques for the OC cryo-mirror as well as for the
room temperature OC mirrors. Some time was devoted to preparing for the
micromachining user run at the end of the month.

**Terahertz:**

With the shortened week and limited accelerator operations, much of the
THz work this week was dedicated to completing scheduling and safety
procedures in preparation for the experiments to be performed by the
group from Brooks AFB.  Also, we have continued work to achieve full
vacuum enclosure of the THz beam for all experimental systems.  Several
additional pieces of equipment necessary for this have arrived and
others have been ordered.\
\
This week also marked the midpoint of the REU program and Megan Ivory
gave an excellent presentation of her work so far.  She has made very
good progress towards characterizing the TK THz power meter, and as is
often the case, revealed other new questions.  We are certainly closer
to being able to make reliable and accurate power measurements of the
FEL THz source though, and have been very pleased with her work on the
project.