# MEMORANDUM 

**To:** Distribution

**From:** George R. Neil

**Subject:** FEL Upgrade Project Weekly Brief -- June 25-29, 2007

**Date:** June 29, 2007

**Highlights:**

We had a productive week despite challenges from competing events at
JLab (a 12 GeV DOE Review) and the attendance of several team members at
the 2007 Particle Accelerator Conference.  The Test Stand Gun chamber is
vacuum baking at 400C until mid next week.  We measured Q0 versus
gradient of the AES 750 MHz cavity at 4K and found it was fine at \> 8
MV/m (it does \~ 25 MV/m at 2K).  This gradient is sufficiently high
that we can test the cavities with a static LHe fill.  We also assembled
two high power mirror cassettes for installation in the optical
transport system. The Laser Personnel Safety Systems for Labs 1, 2, and
6 are down to punch list items.

**Management:**

We received and established accounts for three new fundings: Phase II
award for our JTO Short Rayleigh Range Program, a Phase II award for our
JTO Advanced Outcoupler Program, an award from NASA to support nanotube
studies.

We continued our development of the FEL Vision for the future with
discussions on Life Sciences applications of the FEL.

Preparations continued for a design review of the Florida State
University FEL on July 13.

DoE High Energy Physics has advised Michael Kelley that his proposal for
support of two doctoral students in SRF research has been selected for
funding.

**Injector:**\
The GTS gun chamber is being vacuum fired at 400 C here in the Lab\'s
North Access Building with great success so far. This is the first time
the FEL injector group attempted something like this in-house to desorb
hydrogen from the bulk chamber walls for improved vacuum conditions
during nominal operations. The CEBAF Source Group has experience in this
process and we are thankful to Phil Adderley and Marcy Stutzman for
their input. The choice of using electrical heating elements to make a
convection oven instead of the forced air heaters used before has proven
to be a great success. The temperature ramp up in 100 C steps was very
smooth and the temperature holds perfectly steady, with a maximum
temperature difference of 5% across the chamber. We will use this
technique for further FEL and GTS guns vacuum bakeouts. The GTS chamber
will soak at 400 C for a few more days. The advantage of doing the
vacuum chamber in this way is to desorb hydrogen from the flanges and
their welds along with the chamber walls. We used to vacuum fire the
chamber before welding the flanges at 550C for 24 hours in a commercial
vacuum oven outside the lab.\
\
Don Bullard is almost done with the anode plate polishing after coming
up with a new polishing recipe for molybdenum, which is much harder than
stainless steel. He has completed the outer radius and expects to finish
with the inner radius by next week. We are expecting any time now quotes
on final polishing and optical coating from two companies.\
\
We had a GTS vault walk-through with the Safety Systems Group prior to
the PSS and LPSS design and to prevent any installation conflicts with
the rest of the hardware being installed.\
\
The FEL gun is being disassembled for thorough cleaning and
refurbishing.

**RF:**

In order to better understand our options for the installation of the
AES cryomodule in the Gun Test Stand we did a series of measurements of
one of the 748.5 MHz cavities in the SRF departments Vertical Test Area.
The cavity was tested at 4K, at 2K and again at 4K. The results are
shown below. In the first 4K test the cavity quenched at 10 MV/m,
meaning that it would probably operate at 9 MV/m in the cryomodule. We
then tested it at 2K to insure that it was not an anomaly with the
cavity surface that was limiting us rather it was the average heating.
When we did this the cavity processed at approximately the "same" (with
error bars) gradient and jumped out to 22 MV/m. In the end the cavity
made 25.5 MV/m limited by RF power, i.e. concerns that pushing the RF
power higher might damage an expensive cable within the test stand. In
the second 4K test the cavity did not quench rather it was limited by
forward power of the RF source of 300W. The error bars are larger on the
4K measurements because the RF power coupler was optimized for 2K
operations. Although there is the potential for operation at slightly
higher fields these tests lead one to conclude that this cavity could
operate safely at 9 MV/m at 4K.

![](media/image1.wmf){width="5.990277777777778in"
height="4.097222222222222in"}

Figure 1. Vertical test results for cavity AES-SC1 operated at 2K and
4K.

In other activities:

RF -- Purchasing was given the OK to purchase 3 solid state RF 2 kW
amplifiers at 748.5 MHz.  We are saving considerable budget compared to
using the lower Q~L~ coupling and IOTs or klystrons. Delivery is
scheduled to be in 12 to 14 weeks ( around October 1^st^).  The AES
cryomodule is not expected to be assembled and installed until around
the end of December.

Two expiring SOPs (Buncher & Linac) were updated and re-issued.

GTS Gun HVPS -- The Drive and Measurement stacks were cleaned and are
ready for additional testing next week.  The HVPS will be driven to
about 150 kV under no load, to 5 mA with a short circuit, and to about
30 kV at 5 mA under a resistive water load.

**Instrumentation and Controls:**

Again this week the Laser Personnel Safety System (LPSS) and the Gun
Test Stand (GTS) took center stage. The work in labs 1, 2, & 6 is
complete except for punch list items. Work in labs 3A & 5 is now ramping
up. The software for the master LPSS controller is also making progress.
The transition from VME GPIO modules to PLC controller link is
progressing well; initial communications and test should begin in a week
or so. The students have worked fidelity issues with the sound playback
modules this week and installed them in labs 1, 2, and 6.  To eliminate
the sound distortion, the input file was modified and the input analog
signal was filtered between 190 Hz and 3 kHz.  This was done to
eliminate aliasing while recording due to the difference in sampling
rates between the input file and sound chip.  Additionally the output
load on the sound board was modified.  Extra sound chips have been
recorded and installed on sound boards and the modules are plug and play
ready for the other labs.\
   Most all of the components for the GTS SF6 gas transfer system are
now here. Fabrication of the support panels and bracket has begun. The
cutting, sweating, cleaning, and mounting of the copper piping will
begin late next week continuing into the following week. Some progress
has been made on the High Voltage Power Supply Controller for the GTS. 
We\'ve reviewed the Analog card design, so we are moving forward with
the board layout and routing.  The PCB is 90% completed and only a
handful more of components need to be placed.  This was delayed due to a
hard drive failure on the computer used for PCAD applications.  Since
all of the files work directly off of the highly protected and backed up
network drives no data was lost.  The drive was completely formatted and
recovered.  Some final settings need to be modified but the computer is
up and running.  With this computer back online the layout will continue
today and be ready for error review early next week.\
   Progress is being made with the Sextupole Magnet testing in the
Magnet Test Area.  The IOC is configured and is up and running.  All of
the electronics are ready for use and the only thing that still needs to
be done before testing can commence is the CAN communication between the
power supply and the IOC.  The hardware for this is all configured and
ready to go, it just requires some time to tie this into the system. 
Major progress has been made on the Beam Viewer Control Cards.  12 cards
are nearly completed and these will be used to control the viewers and
other insertion devices within the GTS.\
   Also this week collaboration efforts continued with for the 12 GeV
portion of the CEBAF accelerator.  We\'ve been communicating about
upcoming BPM electronics\' designs for 12 GeV.  The embedded BPM
electronics design was presented and the methods for measuring beam
positions in CEBAF accelerator.  This team effort will provide us with
another test environment for BPM electronics\' designs as well as
outside suggestions and feedback.\
   This week has also been spent working on the wiki website. A table
for ALL the existing Beam viewers and Quad Magnets has been made. They
are all in table format and easily editable. We have also begun the
search to find an easier way to make the flags for each more user
friendly. Finally, we have completed labeling all but 12 of the machine
pics we have of the laser itself and now have organized them. We plan on
having them labeled on the wiki within the next few days. A link between
the pictures and the item itself is being worked so that if you want to
look at a specific beam viewer it is easy to check its status, see its
actual item description, or view a picture of that specific viewer.

**High Power Optics Risk Reduction**

This week we made progress in the various areas discussed in last
week\'s report. The in-situ transmission measurements on the outcoupler
(OC) mirror for the High Q test are awaiting some calibration data that
is being taken down in User Lab 6. We are using the hutch in that lab to
do calibration of the spectral response of the scattered light from the
2.8 micron mirror used for the harmonic content measurements. This is
not easy to do, as the total integrated scattering (TIS) won\'t be high,
and we are measuring the scattering 30 deg, well off normal incidence.
Nevertheless, we believe we got the data we need.

The scientist responsible for doing the microscopy on our damaged 2\"
outcoupler mirror, Dr. Olga Trofimova, went through the images obtained
with the Hi-Rox microscope with me. The images clearly show that the
mirror was accidentally contaminated when the laser mode was mis-steered
and intercepted some heat-conducting paste. With the incorporation of
the new scatter shields this will not happen again. The mirror will now
be sent to our collaboration teams for further analyses of the coating,
both in the damaged and undamaged regions.

Great progress has been made on the creation of a user-friendly input
screen for the open source optics program OPC. It now accepts up to ten
optical elements, and displays a plot of the intensity cross-section on
the same page. We will be giving it a thorough trial over the next few
weeks.

We have prepared a draft of the FY08 Annual Work Plan for the high power
optics risk reduction tasks and are now discussing it with the
principals to ensure they are comfortable with it.

**Optical Transport:**

Activities this week centered on preparing the optical and delivery
components for the two new high power Labs. Both of the mirror stages
are vacuum cleaned and assembled. The wiring for both the stepper motors
and limit switches is complete. We will wait for the completion of the
Laser Personnel Safety System in Lab 2 to test the motion. Six broadband
silver coated mirrors were pasted to backplane coolers. Theses include
populating one of the three possible mirrors on the stage, one for the
turning mirror above the stage and the third for the Lab Shutter. The
modeling for the Lab insertable water cooled transport mirror is
complete.

**Lasers and Optical Diagnostics:**\
Most of the parts for the Gun Test Stand (GTS) drive laser system have
been ordered. Further effort was made to lower the cost of the laser
amplifier. We modified the pulse synchroniza-tion and control system for
compatibility with both new and some old in-house equipment for the
upcoming test. The parts have been ordered by I&C group. We are
preparing a fast pulse selection system but delayed the test due to
safety concerns over the obsolete HV cable connectors found on the pulse
generator. The design of the optical transport is near completion and we
are getting the needed optical parts ordered. We were informed there
will be a long delay on the fabrication of optical table assembly due to
the busy schedule of the Lab's Machine Shop. We are trying to solve this
issue by finding another manufacturer.

**Terahertz:**\
This week we worked on activities related to the FSU-FEL THz beam
transport system.  We are working with IR camera vendors to make an
appropriate choice of bolometric array with which to construct a THz
camera.  We intend to have our own camera ready when beam is restored.

**Word version:** [FEL Upgrade Project Weekly Brief -- June 25-29,
2007](http://www.jlab.org/accel/fel/documentation/07weeklybriefs/upgradeweek07jun25-29.doc)