# MEMORANDUM 

**To:** Distribution

**From:** F. Dylla/grn

**Subject:** FEL Upgrade Project Weekly Brief - September 4-8, 2006

**Date:** September 8, 2006

**Highlights:**

We spent the week performing User tests and making calibration
measurements on the short Raleigh range operation.  FEL Users performed
tests on a THz spectrometer which offers the possibility of single shot
bunch length measurements and exposed jellyfish to UV light using a
laser on loan.   We had less success with a detector calibration run for
the Dahlgren group when our optical transport system had a motor
failure, which prevented delivery of beam to the lab. We held a kickoff
for our two JTO efforts: Short Rayleigh Range FEL Operation and Advanced
Mirror Figure Control.

We also want to wish our Chief Optical Scientist Michelle Shinn a very
happy milestone birthday!

**Management:**

We held a kickoff for two JTO funded efforts with ONR and JTO
attendees.  One effort involves the measurement of FEL performance under
short Rayleigh range conditions, a situation that Bill Colson has
predicted to provide reasonable performance in contrast to 1D
predictions.   Our second effort involves the design of an outcoupler
mirror with variable radius of curvature.   We reviewed the technical
approach, schedule and budget plan.  This efforts got started quite late
in the year but we intend to recover lost time by an aggressive schedule
this fall.

 

We held several meetings to plan efforts for our two week down
period which starts next Monday.  The main effort of that period will be
the installation of the cryogenic outcoupler and its associated helium
lines.  With this system in place we cannot change to mirrors for other
wavelengths so the installation will only be to verify the improved
performance one gets from the cooling before removing it again.  We
anticipate testing the mirror with FEL beam in about two weeks.   There
are a large number of other maintenance and improvement items on our
activity list involving nearly every system in the FEL in addition to
the mirror change.

 

**Operations:**

We had a short week, with Ernesto recovery and user runs leaving little
time to dance naked in the field of the mind (to quote Kary Mullis\...).
Monday, we celebrated labor by not working. Tuesday we processed the gun
after recesiation and recovered from various storm-associated issues,
but eventually got to recover a 1 micron lasing setup in preparation for
JTO studies. Wednesday was to be devoted to a Dahlgren user run, but
problems with the optical transport system precluded any meaningful
work. Thursday we ran for THz users, and interleaved some machine
improvement activity. We pushed current to clean up the cryounit & check
BBU (we worked up to 4+ mA CW at 37.5 MHz before running out of both
time and intestinal fortitude). We also performed a \"machine
restoration\" test, wherein we checked some phase advances and betatron
amplitudes, then loaded a sequence of several arbitrarily selected all
saves, and rechecked the phase advances and amplitudes. Reloading the
allsaves crashed one of our legacy (a flower of early 1980s technology)
trim racks, thus providing a real-life flavor to the whole affair.
Needless to say, the machine didn\'t recover; the orbit was hosed by the
trim rack fault and the focusing also didn\'t come back, with minor but
evident shifts in the phase advances but amplitude changes of perhaps
20% - corresponding to beam envelope shifts of order 40%. Our repeated
need for \"matchathons\" is therefore not particularly surprising. These
tests should be repeated with more care and more quantitatively. Friday
we ran for JTO short Rayleigh-range studies, with the 1 micron setup
being extended to steady harmonic lasing at 1 micron (actually, 935 nm),
on the 3rd harmonic of the 2.8 micron mirrors and the 5th harmonic of
the wiggler (set to \~4.7 microns).

**Users:**

We had very successful jellyfish (ephyrae and polyps) experiments this
week. (This was the third in a series of experiments to determine order
of magnitude bounds of UV and THz light.) This was essentially a repeat
of 355 nm UV from the 4 Watt laser in Lab 4. Exposures were for 300,
600, and 1200 kJ/m2. But in this set, in addition to simply observing if
there was a change in ephyrae behavior, here free radicals were
monitored as a function of UV dose. In addition, we are gaining
experience in dose delivery to live systems, experience needed for
future BioScience research such as the melanoma study proposed by the
Biomedical Photonics Consortium.

**WBS 4 (Injector):**

On Monday we re-cesiated the photocathode which had delivered 27 C and
63 hours of beam time for FEL ops since the previous recesiation. Since
Monday\'s re-cesiation the photocathode has delivered 41 C and 14 hours
of beam time. We have been re-cesiating more often due the low SHG drive
laser power (the drive laser rod will be replaced during our upcoming
maintenance).\
\
We continued high voltage processing the test electrode coated with the
field emission suppression film by Nimel Theodore from the College of
W&M. The results are encouraging so far. The electrode has been
conditioned to 105 kV and 26.25 MV/m with field emission current below
the detection level. The maximum electric field in the FEL photocathode
gun is 12.4 MV/m at 500 kV.\
\
We held a kickoff meeting with Dr. Ravi Joshi and his student Deepesh
Kumar Koppunuru from the Dept. of Electrical & Computer Engineering at
ODU to start a two year collaboration for a MS thesis, extending the
PARMELA model to the entrance of the FEL wiggler for further
understanding of Longitudinal Space Charge effects.

**WBS 6 (RF):**

No activity this week.

**WBS 8 (Instrumentation):**

This week was shortened by the holiday (& lengthened by the hurricane),
recovery was rather painless -- thankfully! We continued to investigate
the cause of the varying momentum spread by installing electric field
and magnetic field antennas on several different view ports in the 4F
region. It is quite easy to turn this effect on & off so we are hoping
to eliminate various chamber discontinuities as the source of this
problem.  So far we have looked at the 4F07 viewer and the Upstream
OCMMS port and have seen no evidence of a source.  We are also setup to
look at the Downstream OCMMS port during OPs today. Efforts were also
directed to preparing for our scheduled maintenance activities for next
week. Plans are in place for installation of the synchronized timing
distribution system with the first hub going into the 3F region.  Other
timing and video signals will also be installed at the OFO4 for the
multi slit. Additional installation efforts include supporting Optics
with the Cryogenic mirror upgrade. This will include wiring and
connecting cryo diode read backs into EPICS.  A corrector pair will be
installed in the 4F09 region (debunching chicane), channels have been
assigned and additional trim cards have been secured for this.\
  We are preparing a multi-function VME card for application in the
Emittance frame-grabber system. This will be accomplished by using the
previously designed VME carrier board and related modules. Specifically,
we have built-up two of the F0106, 1:4 channel analog distribution
modules and configured them as a 1 in 8 out timing distribution system
using the F0060 VME carrier board. We will complete the project by
adding a F0060 4-channel timing board to the carrier which will be
hard-coded with the fixed delays which are required to trigger the
cameras for the frame-grabber system. We have also recommissioned a test
IOC along with the Altera programming PC.\
  We have prepared the decommissioned Con-Optics 305 synchronous
countdown generator to replace the existing chassis in the drive laser
clean room. This will liberate a fully-functional CO305 for use with the
advanced drive laser in Lab 6. Also, we have started a project to design
a new high-speed analog buffer module. The motivation for this design is
to be able to copy the drive laser\'s EO cell logic pulse in order to
monitor it, distribute it and interlock on it.\
  A major re-write of the epics-2-devlore data gathering tools was done
this week. There are three immediate benefits to the new code. First the
server-load is dramatically reduced which increases the amount of data
which can be exchanged. Second, the data is archived in a much more
efficient way providing smaller archive files and faster data-retrieval.
And third, the ability to launch multiple instances of the tools is now
possible. This allows for a specific, standardized, \"e2d\" applications
to be run for each system. Currently, we have set-up two instances, one
for the web-page strip graph FEL ops graph and another to monitor the
drive laser specifically. We are currently in the process of setting up
a 'chron' process that catalogs the usage of the FEL user labs for the
purpose of automating.\
    Testing was completed on the 4-Ch RTD Monitor Board this week.  We
have one board completely populated and all four channels function as
they should and the on board bus controlling PLD was successfully
programmed and all operates as it should.  We are currently gathering
together enough parts to assemble 20 boards.  We have also received a
quote for time frame and cost of assembly.  With this quote and the
parts kit that we are assembling we should have these 20 boards within a
month.\
    The layout of the 3U General Purpose I/O card is nearing
completion.  There are a couple of issues that are being resolved and
then the quote will be ready to go out.  A parts list for this board is
being generated so the required parts for the prototype can be ordered. 
Another board that is being worked on is the HOM BPM Logarithmic Monitor
Board.  The schematic for the prototype is completed and the layout is
beginning.  This requires some extra time and effort as we figure out
how to impedance match the traces.  The general layout is completed,
some tweaking will need to occur precisely set things up.\
  The FPGA to ColdFire bridge coding is being worked on. When the code
uploaded on the FPGA, the ColdFire couldn\'t boot normally. After
checking, the TEA pin for ColdFire was found to be pulled down by the
FPGA. Changed the FPGA code and set the pins TEA and IRQ3 at high level.
After that, the ColdFire can boot normally with the FPGA. Still working
on the communication between ColdFire and FPGA.\
  Testing of the UHV ion pump power supplies is scheduled for next
week.  The software for the UHVs is ready and has been setup for
iocfel5.  Met with representatives from Freescale and Arrow for a
discussion concerning our future plans for embedded IOCs.

**WBS 11 (Optics):**

#### FEL mirrors

We prepared the cryo-optics for installation next week including the
mounting and brazing activities. On Monday after the part is out of the
oven we will be able to determine if the braze successfully produced a
mounted mirror with low astigmatism.

***Other Activities:***

I would first like to welcome Dave Hardy as the new FEL Safety Warden.
Dave accepted this position on September 1st for a six-month tour of
duty. Shukui Zhang represented the Optics Group for FEL06 where he
presented two papers. These papers are titled: "Longitudinal Phase Space
Characterization Of Electron Bunches At The JLab FEL Facility" And
"Phase Noise Comparison Of Short Pulse Laser Systems".

 Next week is the start of the shutdown period. The majority of this
week was spent on preparing for next week's activities which for the
most part consists of an installation of the Cryo-cooled OC mirror,
aligning and improving the vacuum of the optical transport, and
increasing the output SHG power of the Drive Laser. This week we also
installed two B&W cameras, one on each to image both cavity mirrors.
These cameras have response at 1.06um and will be used to observe the
laser mode for the short Raleigh-range cavity studies. Group members
also supported two User experiments and the JTO kickoff meeting.

**Terahertz:**

![](media/image1.png){width="2.0in" height="2.1256944444444446in"}On
Thursday, we had another good user run in the THz lab. Nick Agladze, who
works with Al Sievers at Cornell, tested their latest interferometer
design. This system generates an interferogram in a single shot with no
moving parts. It's a very clever design and our THz source offers a
unique capability to fully test their system. The figure shows an image
from the tests. The fringes are the interferogram generated in a single
shot on the Pyrocam. After setting up the interferometer and Pyrocam
detection system, we achieved immediately in our first attempt. With the
stable beam being delivered, we were easily able to fine tune the
alignment to produce the best signal. We then performed tests to
properly set the polarization of the incoming beam and the angle of the
polarizers used in the interferometer. These tests optimized the
interferogram signal and we then proceeded to make spectral measurements
as the bunch length was systematically varied by changing the beam
energy. We saw some very interesting results that appear to be
consistent with other machine diagnostics for the different beam
energies. Nick will analyze the spectrum for each test more thoroughly
when he returns to Cornell. We also were able to make measurements of
the THz transmission spectrum for a few samples, including a 350 mm
bandpass filter. We will use these measurements as well as future
planned tests to continue characterization and calibration of this new
interferometer design.

Also this week, Michael Kelley and I (Michael Klopf) presented at the
5^th^ International Conference on Photo-Excited Processes and
Applications (ICPEPA). Michael Kelley gave an overview of the FEL
capabilities and user program. I presented the details of a novel
optical pump-probe technique for measuring nonequilibrium dynamics, and
also gave a brief description of our THz source and user program. There
was a noticeable amount of interest in our THz capabilities and I had
some productive discussions with a few of the conference attendees,
particularly, Xianfan Xu, who presented work on measurements of coherent
phonon excitations in Bismuth in the 1-3 THz range. These phonon
frequencies overlap well with the THz spectrum yielded when we optimize
the bunch compression for THz production.