# MEMORANDUM 

**To:** Distribution

**From:** George R. Neil

**Subject:** FEL Upgrade Project Weekly Brief - March 26-30, 2007

**Date:** March 30, 2007

**Highlights:**

We performed an extensive series of tests of harmonic production for JTO
supported work for SAIC.  We also were able to conclude the week with
some initial measurements aimed at resolving the source and dependence
of CSR and/or longitudinal space charge induced energy spread in our
second arc.  We were also able to provide some beam time after-hours
for the nanotube setup, off resonant optical trap, and Aerospace
microengineering station.

**Management:**

We held two coordination meetings to plan the up-coming installation of
the high Q cryomirror and cooled wiggler chamber.   That installation is
now scheduled to commence late next week barring any unknown hardware
fabrication issues in final assembly of either item.

We worked with lab management to provide DOE with budget requests in
support of a new Infrastructure initiative and reviewed the JLab
response plan for Avian Flu.

We continued work with Integrated Safety Management to assess our
readiness to support the safety audit scheduled for this summer similar
to that recently completed by SLAC.

Michelle Shinn attended a review of the Colorado State University
(CSU) - led proposal on optics and coating development that was
submitted in response to an ONR solicitation

**Operations:**

It was a busy week with operations going into the evening most days.  
On Monday we completed the work on the new 1 micron high reflector and
started setting up for 2.8 micron operations for harmonic studies for
SAIC.  We set up the harmonic energy measurement on Monday afternoon and
took data on Tuesday.  We had one problem with a translation stage for
this setup that prevented us from optimizing the energy throughput
through the slits.  We were able to get data of the harmonic energy vs.
cavity length detuning for harmonics up to the 6th.  We still need to
calibrate the system to get the ratio of the power at the detector to
the power in the resonator.  Once this is done we will have good numbers
for the harmonic energy vs. the  fundamental  We did see a sharp spike
in the harmonic intensity for  the 2nd, 3rd, and 5th harmonics at the
synchronous point.  This is similar to what we saw in the IR Demo.\
  On Wednesday and Thursday we ran 1.06 micron at low power for the FORT
experiment conducted for Old Dominion University.  This was a good test
of the stability of our optical transport system.  We found that the
transport drifted with steering errors on the order of 10 microradians
at the collimator.  We will have to do better than this to deliver beam
for damage tests in user lab 2.  The beam quality for 1 micron lasing
was not very good since the mirror tended to distort  badly as soon as
it heated up.\
 

Wednesday and Thursday evening were spent on running for modulation
measurements in the injector and boron nitride nanotube production in
User Lab 1.  Today we are taking data on CSR/LSC induced emittance
growth in the optical chicane.  We want to be able to compare the energy
distribution in the second arc as a function of the bunching.

**Injector Diagnostic Development**

This week we took a fair amount of data investigating new possibilities
for beam diagnostics in the injector.

We turned on the modulation of buncher gradient, cavity 1-3 and cavity
1-4, modulating different elements at different frequencies, i.e., 3
kHz, 4 kHz and 5 kHz. With very small modulation on the gradient of the
1-3 and 1-4 we got a very good measurable signal in the 0F06a BPM.

We repeated the Drive Laser phase scan. We found again that the zero
crossing of the buncher determined by the new technique we are
developing is different from the zero crossing as determined by our
present procedure. We need to do some data analysis to understand the
difference. To do so, we took additional measurements of the bunch
length at the two different phases of the drive laser. Next we
investigated the dependence of the transverse beam position modulation
downstream of the ¼ cryo unit as a function of the beam trajectory
through the buncher cavity. We clearly can see that a small trajectory
change affects the beam modulation amplitude fairly strongly so that the
effects of the transversal beam kick by the buncher and the energy
modulation by the buncher measured at the 0F06a BPM are comparable.

Finally, a set of measurements was made changing cavity 1-3 phase and
measuring the beam position modulation at the 0F06a BPM. Presently we
are analyzing the data.

**Injector:**

The photocathode gun has delivered about 12 Coulombs and 8 hours of CW
beam time during the week with a QE drop of about 0.5%. A task hazard
analysis for the calibration of the photocathode QE scanner was prepared
and on-the-field practices reviewed by Patty Hunt from the ESH&Q
Division.\
\
***Gun Test Stand***\
Blank Conflat Flanges have been collected and are being prepared to be
mounted to the gun chamber for vacuum firing. We prepared initial
documentation required for the installation of the Personal Safety
System and an initial task schedule. Electrical work and purchase of
components is in progress after power requirements were specified to the
proper parties in the Engineering Division. Hazard analysis
documentation is in progress.***\
***

**Instrumentation & Controls:**

Major efforts continue in the new Gun Test Stand (GTS). Installation of
the network cabling for the GTS control room (room 217) has been
scheduled to begin the week of 4/9. The network switch has been
purchased and configured along with additional patch cables and patch
panels. Work has begun on some light refurbishing of the GTS HV tank.
Since we are designing much of our instrumentation and controls for the
Gun Test Stand around the 3U General Purpose Processor Card and the
Single Board IOC, we decided to make some modifications to the SBIOC
design to make it easier to do some of the simpler functions. We took
one of the blank pcbs that we had and assembled it according to the
modifications. This board with these modifications is currently under
testing. The new gun's quantum efficiency scanner has also been ordered.
This is a galvo unit purchased from <http://gs-scanners.com/>\
Testing continued this week with the 4-Ch Charge/Dump Current Monitor.
Many of the circuits that are used on this PCB are also used on the High
Voltage Power Supply(HVPS) Analog I/O module. Testing was completed on
all of the circuits needed for the analog module and these circuits are
being incorporated into the analog module design. Currently the
schematic for this board is well underway. The overall functionality and
design goals have been planned out so some of the design details are
still being worked out though. The design goals for the Digital I/O
module are clear as well but many of the design details still need to be
cleared up as well.\
To support the High Q Mirror Test, the parts needed to break out the
Silicon Diode Temperature sensors to a precision ADC are all being
assembled and planned out. We have a test fixture assembled to simulate
the diodes at the temperature of 40K and we can track the voltage over
several days to get a noise calibration of the entire system. The
breakout system to patch the required signals into the ADC has been
assembled and is ready for installation. This will be installed along
with all of the cabling early in the upcoming down to get as much time
for the noise calibration and system check out as possible.\
The script for shutting down the FEL has been heavily modified. As the
requirements changed the existing application lacked sufficient
flexibility to easily meet those needs. The application is now highly
flexible and new modes of shutting down can be added without generating
a lot of code. Time on Monday has been allotted to shake out the new
code and determine where changes may need to be made.\
Work continues on the Laser Personnel Safety System. All the door
monitors for the LPSS were installed this week. Additionally, we have
decided it is more cost efficient to design a board for the LPSS PA
system than it is to purchase the pre-made board, so design of the PA
board is starting today. It will utilize the Winbond Chipcorder 17150
package for the sound record/playback. The chip will be programmed using
the Winbond ES17XX_USB Evaluation board. The sound amplification for the
system will be done using the ST-PA6 audio amplifier made by Radio
Design Labs.\
Work also continues on the Single Board IOC. The 20 I/O pins were
connected between the ColdFire and the FPGA and the prototype board was
modified for this connection. The code was programmed for the connection
and loaded on the FPGA. With these 20 I/O pins, the Single Board IOC
will have more functions for digital I/O controls. Also added the
signals (TIP and TS) from the Coldfire to the FPGA. These two signals
are used for Chip Select function that the ColdFire controls the FPGA
through the bridge. The ColdFire-FPGA bridge was updated and loaded on
the FPGA. The bridge works great and the ColdFire can read and write the
data from the RAM on FPGA. The revised Single Board IOC is under
debuging. After the testing, we will make new version and will start to
use it for Beam View control.\
The FELWiki website is now available for offsite access at:
<http://fel.jlab.org/wiki>. Access requires your CUE username and
password as does each users wiki account login for editing. (i.e. no
registration required - just log in and edit) In preparing the new FEL
wiki site, the PHP maintenance scripts were written to generate and
import 12,569+ new wiki articles as \"reserved\" in order to maintain a
1:1 correspondence with the existing Devlore database. Everyone is
invited to add and modify content. Off-site file uploads are also
possible.

**Beam Transport:**

Improvements and Upgrades

*New Gun Test Stand*

•  In calculating the stresses on the flange of the gun chamber when
attached to the SF6 Tank, I have concluded that superposing the many
cases of closed form calculations is very complicated.  I don't believe
I can create a reviewable set of documents. Instead, a FEA analysis
using the ANSYS workbench software can do a far better job.  Mike Bevins
of the Engineering Group led me through a preliminary version of the
flange using an IDEAs model made by Ron Lassiter.  At week's end I have
arranged with Ed Daly to utilize the overview services of Robby Hicks
while I enhance the analysis using ANSYS mounted to Fred Dylla's old
PC. 

•  The Gun Chamber is in a position to be baked as soon as we finish the
new wiggler chamber 

*SF Sextupole Magnet Testing*

•  The Accelerator Division's Power Supply Group continues their
commissioning of the CANBUS control of the new power supplies.  They
have solved the communication problem and are working on getting the
internal ramp to work reliably.  As soon as this is working, Scott
Higgins can complete the control software and we can start our plan to
test the magnets with the power supplies in Magnet Test with the actual
software. 

*Cooled and less resistive Wiggler Chamber*

•  Don Bullard of the Injector Group did a first copper sputter in the
Test Chamber.  The test was not as successful as we hoped.  The test
pointed out the difficulties of maintaining the plasma in the right
portions of the chamber.  The ceramic insulators we used to isolate the
central copper strip also got plated with copper, eventually causing
shoring and instability in maintaining the plasma.  Our conclusion is
that evaporation may be a quicker option.  At week's end we are working
on a demonstration sample.

•  In parallel, the source lab folks made the copper cooling tubes and
the chamber had a solder bead run on the top and bottom edges and
cleaned to eliminate any flux. 

**Optics:**

***FEL Mirror Development***

Measurements of the harmonic content were made early this week and, with
the new configuration, worked well.  We collected data on the energy in
the 2nd through 6th harmonic as a function of cavity length detuning. 
The transmission of the setup needs to be determined before the ratios
can be determined.

Michelle Shinn attended a review of the Colorado State University
(CSU) - led proposal on optics and coating development that was
submitted in response to an ONR solicitation.  While there she met with
two members of the Optics Improvement collaboration.  She also gave an
update to some of the LIPSS (Dark Matter particle search) consortium
members on the FEL performance during the two physics runs, and proposed
future paths.

The work with a student, Anne Watson, on modeling and measuring the
efficacy of apodization on our edge-outcoupled mirror is making
excellent progress.  We are now able to quickly simulate the effect of
changing the feature parameters on the far- and near-field intensity
pattern.

#### Cavity/Optical Transport

This week was primarily devoted to preparing for the 1.6um High-Q cavity
cryo-mirror work. We received two brazed cryo-frames from T. Elliott. Of
the two, one was leak tight and the other had a leak along the ID. The
first we slowly cryo-cycled down to \~80K and the other was sent back
for a second braze. The cryo-cycle opened a leak on one of the cooling
tube to frame junctions and was sent back for another braze run. The
result of the second braze was two leak tight mounts. When they where
cryo-cycled the first remained leak tight and the second now has a leak
along the OD. The later is with T. Elliott for a third attempt. We
received a Boron Nitride plate that was machined to fit the gold target
for reforming. This was placed it the vacuum furnace overnight, we await
news of its success. This target will be used to sputter both the
cryo-frame and the perimeter of the 1.6um optics. A design for a
cryo-diode support that should provide a faster and more accurate helium
temperature readback was sent to the Machine Shop for machining. We
expect to receive it later today. The backscatter shields for both
cavity ends as well as the collimator mirror were received early this
week. We want to thank G. Biallas, who quickly brazed the cooling tube
to the shields. The shields were sent out for laser black, light
absorbing plating. We anticipate receipt late next week. The CPU board
for the Optical Beam Position Monitor was ordered. The vacuum can is
ready for installation. The electronics should be ready by mid next
week. Cryo-diodes were ordered for the cryo-mirror tests. A harness to
bring the cryo-diode signals outside of the vacuum chamber is being
readied. We will have eight helium temperature diodes in the OC vessel.
Half of these are redundant with half for inflow and the others for
outflow. Additional inline cooling water thermometry for the HR is being
readied as the RTDs are very fragile and take a few days to cure.

 

#### Optic's Student Activities 

The majority of activities this week were geared toward preparing for
the upcoming machine down. The pump carts have been pumping all week and
the problem with one of the RGA\'s seems to be fixed. It is believed to
have something to do with how they are shut down. All on our carts are
in working order and test fine.

 

Assistance was also given to C. Gould in association with the cryo
mirror installation. The cryo-frame assemblies were cryo-cycled and
leaked checked during the week. Tools will be cleaned this afternoon in
prep for their use next week, along with gathering of other materials
such as gloves, isopropanol, acetone, etc.

 

#### Lasers and Diagnostics

The investigation and search for a suitable drive laser for the Gun Test
Stand continues. We are searching for one with the lowest possible cost
while keeping the required specifications. We have contacted many laser
vendors. Some discussions were held within the FEL team and a decision
will be made after a bit more work is done. We also held a meeting to
discuss the upcoming EO sampling experiment for bunch longitudinal
tomography and a schedule was made. We have started preparing the EO
sampling laser system for a safe move into location in Lab 3. We
supported the ODU user on their FORT experiment.

 

**Terahertz:**

This week, the new design for the gas cell to be used in Harvey Rutt's
double resonance experiments by was finalized.  The new design allows
the mid IR beam to enter and exit the cell at Brewster's angle through
the silicon windows to eliminate the interference effects from the
spectrum.  The difficulty is that the angle is very severe, making the
design and fabrication of the cell very complex.  We also were able to
make more measurements of the incoherent visible synchrotron light with
the Vigo detector.  This is the detector that is used for measuring both
the mid IR spectrum and to detect the modulation of the spectral
components induced by the THz pulses.  This is important because it
gives us an absolute phase reference through the sample (gas cell or
solid phase sample).\
\
Also, plans were made this week to move forward on the electro-optic
(EO) measurements to be performed in the THz lab.  This will require the
installation of a Ti:Sapphire oscillator enclosed in a local laser hutch
enclosure just outside of the THz hutch wall.  An enclosed beam
transport line will also have to be made to deliver the laser beam into
the THz hutch.  The goal is to make some baseline measurements and to
perform some straightforward EO measurements in the THz hutch to gain
experience that will be valuable in determining how to implement a more
permanent long term system.