# MEMORANDUM 

**To:** Distribution

**From:** F. Dylla/grn/gpw

**Subject:** FEL Upgrade Project Weekly Brief - January 15-19, 2007

**Date:** January 19, 2007

**Highlights:**

The highlight of this week was a two day review of the program and its
accomplishments over the last two years. In preparation for that review
we also completed late last week our annual report for FY06.
Experimental efforts were devoted to establishing stable high power
lasing at 900 nanometers.

**Management:**

This was a shortened week due to the Federal Holiday, but a busy one
with the ONR/ NAVSEA Review on Wednesday and Thursday.\
\
The review was attended by over 50 people, 35 of which came as committee
members or observers.  Bill Colson chaired the committee which included
John Albertine, Charles Brau, Courtlandt Bohn, William Graves, John
Lewellen, Henry Freund, Tom Meyer, Al Skolnick, Gene Nolting, Fred
Marcell, Todd Smith, Lou Marquet, Siva Mani and Al Ogloza. Also in
attendance was our program office from ONR and NAVSEA including our
primary points of contact Lew DeSandre and Capt. Dave Kiel.\
\
The main consensus of the panel was that significant accomplishments
have been made at Jefferson Lab since the last review 2 years ago, which
place us on a new platform - a 10kW tunable laser, from which to explore
future capabilities to even higher power.\
\
The committee also agreed with the immediate list of priorities for the
immediate future and is providing guidance to our ONR/NAVSEA Program
office to develop our task plan for the next 18 months. This effort will
be advancing technology to reduce risk for the planned 100 kW INP
program in FY10.

**Operations:**

Operations this week were mainly devoted to tuning up the laser at 900
nm in preparation for the LIPSS experiment.  We first obtained lasing
with the new 900 nm high reflector on Tuesday.  We found that the lasing
was not optimal but that the power did not fall off too  badly with
increasing current.  We obtained up to 1100 W downstairs.   There was
some evidence of astigmatism in the high reflector.  This will limit the
gain and efficiency a bit.  Since the performance was not very good we
started to tune up the electron beam by doing a  complete injector
setup.   On Wednesday and Thursday most of the first string operators
were involved in the ONR review so the second string was sent in to get
some experience in setting up the accelerator and optimizing the laser. 
Operations were delayed on Wednesday by a failed air compressor.  The
beam was phased up but the operators were not able to get the laser
going.  On Thursday the operators phased up the accelerator and did get
the laser up and running.  We found that more power and stability could
be achieved at a requested wavelength of 0.94 microns.  This was sent to
user lab 1 for boron nitride nanotube studies.  Today we are working on
getting the electron beam better matched around the machine so that we
can get better performance from the laser.

**WBS 4 (Injector):**

The DC photocathode gun has delivered 55 Coulombs since the last week\'s
re-cesiation. We presented a talk before the ONR/NAVSEA Review Panel
about the status of the DC photocathode gun and the Gun Test Stand. D.
Bullard continued solder testing on the wiggler mock-up chamber and
demonstrated that the chamber does not warp by application of heat for
soldering by mapping out the chamber surface before and after the
soldering process. He also assisted G. Biallas soldering water-cooled
mirror mounts. We have received all the pieces for the new motorized
stalk retractor system. This system will be incorporated to the existing
FEL photocathode gun during the maintenance shutdown to shorten the
re-cesiation time from 3.5 to 0.5 hours. N. Wilson presented a layout
for installing the hydraulic cylinder to slide the shield door in the
Gun Test Stand.

Gun HVPS - The HVPS is fully operational and working on both driver
stacks with no problems.

**WBS 6 (RF):**

RF - The system is fully operational.  The RF system is experiencing 2
minor problems.  The first are false positive faults with the Arc
Detector sub-system.  This trips the machine off about once or twice a
day and is easily reset, causes some lost time and aggravation for the
operators.  The second minor problem is Cavity Waveguide Window
Temperature (CWWT) faults with several cavities.  This fault trips the
machine also, but is easily reset and the fault masked if the CWWT
signal is prompt with the e-beam.  This means the CWWT signal is due to
RF power coming back up the waveguide and not due to the cavity window/s
heating up.  Vacuum signals provide cavity window protection also, so
the windows are not completely unprotected when the CWWT faults are
masked.

**WBS 8 (Instrumentation):**

The already short week included last minute preparations for the FEL
NAVY review, running data for the entire 10 year history of the FEL
project was compiled (online at:
<https://laser.jlab.org/feldoc/JlabFEL_OPS-vs-Time.pdf>). Work continues
to understand the operation of the Golay cell and associated detector
electronics. We use this wide band detector for the bunch length
measurements with the "Happek device". There are numerous diagnostics
applications with the coherent synchrotron and coherent transition
radiation for this type of detector but of the 4 detectors that we have
the 1 is fully functional, 1 is dead and the other 2 need repair. The
problem is that there is no documentation or service available. We have
identified and understood many issues with the detectors we have,
and are working on an improved version of the electronics to be used
with the detectors. 

    Some work has been performed on the conceptual design of the High
Voltage Power Supply and the Charge/Dump Current Monitoring system that
will be used in the GTS.  These systems are being designed to be pin-pin
compatible with our existing systems while using our Single Board IOC
and our 3U General Purpose Processor Card.  With this combination we are
exploring the concept of combining several systems into a centralized
crate to reduce design costs and to better utilize available real
estate.

      In addition to attending the review, we have continued the EO cell
investigations this week. Using a spare 25D rf driver which is known to
be good, we have placed the spare driver in various configurations to
try to further isolate the effects, the results are unclear and further
testing will be focused on the EO cells themselves. In the mean-time we
are analyzing the archived data of the EO cell bias setting versus
various duty factor settings. This work is ongoing, but is happening in
parallel with the hardware testing. Also this week, we have identified
two features of the existing drive lase pulse control software that can
be refined to improve operations. We have also been working to introduce
the use of the new \"fella\" operations and CUE accounts.\
    During the Injector phasing this week we finalized the procedure for
how to properly setup the injector.  This procedure will now be
available for public use.  After the Injector setup, we established
lasing at 900nm.  While the FEL review was taking place, we used to
machine time to further train our staff.\
    For better software control, MEDM screens and related scripts are
being packaged with the EPICS applications. This will ensure that in the
event of a rollback the screens related to the application correspond to
that particular version.\
    Some time was spent working with our mechanical design student on
the physical specifications for the Flipper Interface Board. With these
physical specifications and the requests of the optics group the
interface circuit was designed.  Once the design was completed the
schematic and the PCB layout were created.  The Gerber data was reviewed
by the manufacturer and then 20 pieces were ordered.  We were able to
get 20 pieces for the cost of 10 which will give us ample spares and the
flexibility to deploy these boards in other generic applications.

**WBS 9 (Beam Transport):**

***Improvements and Upgrades***

• Concerning work on the second wiggler chamber, we made a test chamber
and found that we could attach the copper tubing to it using Eutectic
157 and the chamber did not distort.

•  In work for the New Gun and injector Test Stand, McAllister Technical
Services continues fabricating the stalk retraction mechanism. The
fabrication continues for the aluminum shell that covers the apparatus
at the high voltage end of the ceramic stack for both the injector test
stand gun and the new upgrade to the gun in the vault.

• With regard to removing magnetic anomalies from the beam line, the
remaining item is the studs that hold the field clamps in the GW dipoles
of the Optical Chicane.  Those parts are ready, but we will not install
them until the shut down because the action may disturb the existing
match.

Experimental program

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

•  The LIPSS Group has a loaner version of the new camera.  The camera
was checked out and our existing, proven software can be used with it. 
Several hot pixels are identified and dark current and read noise meet
the tight specification.  We have also proven we can focus a 900 nm
light beam to 5 pixels.  The camera enclosure box was mounted and proven
to be 900 nm light tight.  (Our tests show that black silicone caulk and
black electrical tape are somewhat transparent, but a caulk for masonry
is totally black.)  The remaining 2-inch diameter cooling disk
assemblies were soldered/assembled.  The 8 mirrors for the system (7
require water cooling) are all mounted to their respective mirror mounts
and are ready to be mounted to the optical bench and the turning mirror
stand.  Pico motors for the first two mirrors and the collimator mirror
and camera lens stages are checked out.  We will start the run on
January 29 with possibility of being ready for some preliminary beam
late next week. The vacuum group reports vacuum levels in the two magnet
chambers are in the 10^-6^ Torr as a minimum, considerably better than
we need. 

**WBS 11 (Optics):**

This short week was dominated by the FEL Review. A laser diode pickoff
assembly was built this week. This assembly will be used for the RF
phase monitor that will be installed below the injector light box. Work
continued on the Optical Beam Position Monitor (OBPM) spindle motion and
translation software. This functionality will be split between two
microcontrollers. A design for shielding the two and three inch diameter
cavity mirrors is complete. Several cavity mirror substrates are
currently being qualified. These will be sent off for coating for use in
the high Q cavity test. The EO cell driver for the advanced drive laser
was moved into the clean room and is being used by the Antares laser to
investigate and resolve pulse instability found during the FEL
operation.  We are searching for alternatives to improve the present
pulse control system. We assisted the injector group with the QE
measurement system. The ODU YAG laser in user Lab6 was certified.

# FEL Mirror Development

As mentioned in the Operations section, we started lasing on the
newly-installed 900 nm mirror set.  In situ loss measurements are
ongoing.  The Annual Review gave us the opportunity to meet with Prof.
C. Menoni of CSU and A. Ogloza of China Lake.  We held discussions of
optical coating metrology as well as angle-resolved reflectivity
measurements (BRDF).  We\'ll start collecting samples to send out next
week.

Two 3\" sapphire mirror substrates were qualified and were sent to our
coating vendor for application of a low outcoupling (3%) 1.6 micron
coating.  This will allow us to drive the intra-cavity irradiance to
very high values to cross-check our other measurements.  As a reminder
to our readers, we have designed the current cavity mirror/wiggler
combination to produce a fairly short Rayleigh range (70 cm) so we
\*don\'t\* have a high intracavity irradiance.  Hence, we really
haven\'t collected too much data on the high irradiance effects
since the optical klystron was removed a couple of years ago.  We
learned from our JTO representative that both proposals (Advanced Figure
Control and Short Rayleigh Range studies) were approved for follow-on
funding.

**Terahertz:**

Most of this week was dedicated to the ONR/NAVSEA review, which is
detailed earlier in this weekly report, but we also finalized the loan
agreement with FLIR/Indigo Systems to test a new camera system for THz
imaging.  We hope to receive the camera next week.  Also this week, we
were able to locate a source for silicon lenses that we think will
provide better imaging than we were able to achieve in our previous
tests.  It is our intention to perform imaging tests with the new camera
over the next few weeks.