# MEMORANDUM 

**To:** Distribution

**From:** F. Dylla/grn

**Subject:** FEL Upgrade Project Weekly Brief - August 14-18, 2006

**Date:** August 18, 2006

**Highlights:**

This week the operation of the FEL Upgrade was devoted to three
different user groups.

On Monday-Tuesday, a user team from the University of Maryland (Ralph
Fiorito and Mike Holloway) was given time to test their new electron
beam diagnostic based on optical transition radiation. They were
successful in obtaining some high quality data that is described below.

On Tuesday we set-up the machine to provide high power THz to the THz
User Lab

for the remainder of the week. On Wednesday and Thursday a user group
from the Brooks AFB performed a series of experiments to quantify the
bio-damage thresholds

exposure to THz. These limits are yet to be established and the work is
best done at Jefferson Lab because of the power available (\>10 watts)
compared to lab sources (\~milliwatts). The preliminary experiments that
were done this week used so-called "phantom" models of human skin to
assess thermal exposure limits. The Brooks team was satisfied with their
preliminary measurements.

On Friday, the first THz measurements were accomplished with real
biological samples.

Frank Lattanzio and Dorothy Spangenberg from Eastern Virginia Medical
School (EVMS) designed and executed an experiment to look for THz
exposure limits of jellyfish polyps-using the species that is very
common here in the Chesapeake Bay region-the "moon jelly" (Aurelia
Aurita). This preliminary experiment was set-up to generate information
on THz exposure limits to these tiny animals and also is useful to
develop methodologies for future bio-experiments using the FEL.

The first equipment for the Yale University-Hampton University axion
search experiment was installed in User Lab 1 this week.

Next week we will be doing some FEL gain/loss measurements related to
our JTO grant on short Rayleigh range effects. At midweek, we will setup
for a return visit by Dr. Rox Anderson from Harvard-Mass General
Hospital who will continue his experiments on differential heating of
tissues in the near infrared (@1.6 microns).

**Management**

We participated in a national peer review of the project management
systems we use here at Jefferson Lab for all large construction projects
including most of the activities done in the FEL Department. The Project
Management Office received high marks from the evaluation team.

Following last week's meeting with ONR/PMS-405 management, we completed
and delivered the paperwork for a change request that re-baselines the
FY05-07 work scope according to the available funding in FY05-06.

George Neil and Kevin Jordan spent the week at Daresbury Lab (UK)
helping the 4GLS project team commission their dc photogun-which is
basically a copy of the gun we have in operation at the FEL Upgrade.

On Thursday, were pleased to host a short tour and briefing at the FEL
Facility for Virginia's Deputy Secretary for Education, Ms. Dietra
Trent. We are grateful for the support that the Commonwealth of Virginia
gives the FEL Program annually for funding FEL user teams involving
Virginia universities and industries.

**User Reports (More Details): **

1.) U. Maryland OTR interferometer test:

This week another test of an OTR interferometer was conducted by the
group from University of Maryland. This is a novel electron beam
diagnostic system, which is under development. The interferometer can
provide information about the beam divergence and the beam size
simultaneously, thus when placed in the electron beam waist it can be
used for the transverse emittance measurements. The Maryland group took
a lot of data with beam and is analyzing the data now. We have learned a
about the practical use of the system and its sensitivity to the
realistic beam conditions. Preliminary data analysis by the Maryland
group shows the normalized emittance value \~5 mm\*mrad, (a preliminary
number). That is a reasonable emittance value and is fairly close to the
numbers we have measured previously.

The figure shows the interference pattern obtained during the
measurements. The pattern is used to determine the beam divergence.

![](media/image1.png){width="2.375in" height="2.4805555555555556in"}

2).  Brooks Air Force Base THz Bio-Damage Measurements

Six people, from the division that studies the effects of non-ionizing
radiation on humans, came to study THz interactions with tissue
surrogate material.  They studied 3 different phantom materials at
differing power densities, and times of exposure.  THz light was
delivered in the range 1-10 Watts into a 7mm spot size.  The temperature
rise and recovery of the samples was studied as a function of time,
power and power density.  At the higher power levels damage was observed
commencing in roughly 10 seconds.  A full report will be presented here
after analysis.

**WBS 4 (Injector):**

The DC photocathode gun provided pulsed and over 3 mA CW beam for FEL
ops during the week. The drawings indicating the positioning of the new
photocathode gun and the HVPS tank to be located in the new Gun Test
Stand were completed, signed off and sent to Document Control. Drawings
for changing the location of the HVPS tank door hinges were also
completed and signed off. We started HV conditioning up to 7 MV/m the
graded coated test electrode mounted last week.

**WBS 6 (RF):**

The SRF and RF systems ran smoothly this week. There were two trips in
zone cryogenic related trips in zone 3. These seemed to be caused by
detuned cavities that were drawing excessive power and exceeding the
cryogenic capabilities with the then current setup. Adjustments were
made to the heat load set point such that the resistive (cryo) heater
power was reduced. The cryo heaters and calculated RF heat load are
balanced such that the total cryogenic heat load is a constant. We will
continue to monitor this zone.

We started the process of developing a phase monitoring system for the
injector and potentially some of the cryomodule signals. Experience in
the CEBAF injector has been that such a system is invaluable in
stabilizing the phase drifts which seem to be hampering smooth
operation, especially during the hot summer days. Most of the material
for such a system has been ordered and it is hoped that we can begin
installing the hardware during the September down.

**WBS 8 (Instrumentation):**

In preparation for the General Purpose I/O 3U card design, all of the
parts are being organized in PCAD so the schematic layout can begin. 
Some progress has been made on this project as time permits.  This is
card will be used to distribute the Single Board IOC module signals to
provide both Analog I/O and Digital I/O in a 3U package.  We have
designed the Beam Viewer crate upgrade around this card.  This will also
provide a replacement for the CAN-BUS DSP module.  The pin outs for the
rear connector and the Single Board IOC socket have all been established
and these connections are being established within the schematic.  We
are making progress with the Single Board IOC modules.   Some work has
been completed on the Beam Viewer Control Card this week as well.  The
firmware files to control bus addressing has been completed and
simulated.  The logic all seems to be correct according to the
simulation.  The program will need to be mapped to the PLD on the card
and then tested with actual hardware.  All of the software needed to
develop and program PLDs has been configured correctly on another
machine so we can move forward with the testing of the RTD board as
well.\
   We\'ve successfully powered up the FPGA and Coldfire off of a single
+5 volt supply which allows this card to deploy into various designs
with a single supply voltage. Tested began with the communication
between the FPGA and external ADC along with the timing of the trigger
and sample. All of the four channels are operational.\
  In support of the advanced drive laser test setup in user lab 1, a
high-speed analog buffer is being built to send a copy of the drive\
laser pulse controller signals to the user lab. This will also solve the
triggering problems we have had with the drive laser tek scope.\
   The EPICS application for the UHV ion pump power supplies was setup. 
The code was upgraded and documented.  Also the correct DB9 to RJ11
connectors were made up.  Preparations are being made to install a set
in the FEL and a couple of pairs in the Gun Test Stand.\
   Support for the THz users was given this week in Lab 3. Brooks AFB
was here Wednesday and Thursday exposing various materials to the THz
beam generated by the FEL. Generous amounts of samples were taken from
moist chamois to a ballistics type gel. Basic setup also took place for
the jellyfish experiment today. A 2-axis stage has been moved into Lab 3
in preparation for this experiment. Cable was run for the needed
controls for this stage. Three additional stepper motor cables have been
run into Lab 3 and are being terminated at the moment.\
    An area cam was also added outside the \"hutch\" in Lab 4. Cable was
pulled to the video switcher to the camera and the electricians need to
come and open a distribution box for us so the camera can be plugged
in.\
Organization of the inventoried PCB boards has began. All unpopulated
boards have been organized. Assembly of the SLM enclosures also
continues. Assemblies can be completed as soon as the mac valves and air
exhaust mufflers arrive.

**WBS 9 (Beam Transport):**

#### IR Machine Operations

•  In work for the New Gun and Injector Test Stand, the stalk retraction
system remains on order.

•   The Shop welded the second wiggler chamber. It is now being measured
for conformance to the right geometry.

•  For fixing the problems associated with any heating of the Wiggler
Chamber and associated movement of the OCMMs, we still plan to rigidify
the downstream end and let the upstream end float in a defined way. Joe
Gubeli added that the existing optical tables don't have to be moved
with the new scheme, but rather that the turning mirrors have only to be
switched from the inside to the outside of vacuum vessel and enclosed in
a dust protective environment.

•  Magnet Test is continuing SF sextupole measurement.  The Accelerator
Electronics folks added the reversing switch to the power supply. The
shop completed a set of measurement fixtures that will allow us to
quickly measure any errors in the pole placements that could have come
about as a result of shipping impacts on these cores.  The first
measurements were run to attempt to re acquire the original measurements
on #11.

•  I worked on the scheme to add an additional corrector pair in front
of the Debunching Chicane. It will need a making a mount for the
correctors and a fixture to push the chamber downstream.

• The brackets that will aid us in adjusting the waveguides leading to
zone 3's cryomodule are in manufacture.  This installation is planned
for the September Down Period.   

• 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*  

• Three sets of pole tip extenders and the turning mirror stand continue
fabrication in the JLab Shop, due next week.  The GW magnet stands were
delivered and started installation.  Unfortunately, an error in the
drawing for the stationary stand required that it be shortened by 4
inches.  A vendor will complete the change by Monday, in line for
alignment on Wednesday.  The cooling plates for the 2 inch turning
mirrors parts are complete and will be brazed next week.  The tube
through the second set of dipoles and how to mount the CCD and make it
into a camera are in discussion. 

**WBS 11 (Optics):**

#### FEL mirrors

As a reminder of last week\'s report, as part of our optics improvement
program, we specified a variant of our 1.6 micron HR mirrors.  This
mirror has an aluminum base layer, and then a carefully designed
dielectric stack that essentially reflects all harmonics up to the 5th. 
These could be used downstream of the wiggler, as the aluminum layer
then reflects the incident THz radiation rather than let it be absorbed
by the substrate and underlying ROC control.  We received these mirrors
and they are going through our metrology suite.

For our laser-based optical metrology setups, the I&C group connected
the hutch interlocks to the laser personnel safety system (LPSS) and
provided jumpers from inside the hutch to the stepper motors for the
laser damage tester.  We need to provide them with connectors to our
stepper motors to finish.  Next week we\'ll install the beam transport
optics.

We had Prof. Y. Wu from the Duke University FEL program tour the labs
where we do optical metrology.  The Duke FEL is working in the UV and
DUV portions of the spectrum, and we plan to collaborate with them as we
begin operating in that spectral region.

***Other Activities:***

We continued progress on the cryo-mirror project.  Chris Gould finalized
designs for a number of components, in particular the macor thermal
break.  This part will be manufactured by an outside vendor and
delivered before the end of August.   Other components should be
complete by the end of August, leaving approximately 10 days to prepare
a 3\" optic for installation at the FEL, tentatively scheduled for
mid-September.  In the meantime, testing of an in-house 2\" mirror with
cold nitrogen gas can begin at the mirror test stand, looking for
anything unforeseen related to cold mirrors.\
\
On other fronts, (1) the drive laser was re-aligned to increase power
(thanks Shukui).  The laser cavity seems to be drifting slowly over the
summer. The EO cells were checked, the second cell was causing beam
instability at high repetition rate CW running. This EO cell will be
replaced when a new cell arrives. (2) Shukui continued his study of gain
switched diode lasers, this time using a step recovery diode (SRD) at
low repetition rate 75 MHz. The SRD produces a better pulse shape, but
the phase noise is higher compared to 750 MHz operation and optical
pulsewidth is still longer than expected.

\(3\) a meeting was held to discuss plans for installing the advanced
drive laser into the accelerator. Near term focus on identifying action
items.  At the moment, Shukui concentrates on installing an EO cell at a
low power region of the ADL, to eliminate thermal drifts at EO and
hopefully create better extinction of ghost pulses.

**Terahertz:**

It was a particularly busy and exciting week in the THz lab, with two
user groups performing tests testing the exposure effects to a high
power THz beam.  The Brooks AFB group arrived to complete all of their
training on Tuesday and to begin setting up their experiments.  In
preparation for this, we performed numerous focus tests to characterize
the THz beam profile before performing exposure tests on the tissue
surrogates.  The exposure tests were performed on Wednesday and
Thursday, and in spite of having to deal with a power failure, the
machine operators all did a great job of recovering the beam and keeping
us on schedule to finish the Brooks tests within their allotted beam
time.\
\
The tissue surrogates were all synthetic materials that have been used
extensively for exposure tests at other wavelengths, and the tests
involved measuring the temperature rise during the exposure using a FLIR
camera.  Visual analysis was also performed by several of the team
members independently on each exposure.  Their initial observations with
respect to the temperature rise and damage levels indicate power levels
similar to our calculations.  In the end, the tests went very well.  We
were able to complete all of the scheduled tests and much was learned by
both the Brooks group and us to help prepare for the next phase of
tests.\
\
The week is wrapping up with the first biological tests in the THz lab
where Frank Lattanzio is exposing Ephyrae jellyfish and polyps to
different levels of THz power and analyzing their response after the
exposure.