# MEMORANDUM 

**To:** Distribution

**From:** F. Dylla/grn

**Subject:** FEL Upgrade Project Weekly Brief - November 27-December 1,
2006

**Date:** December 1, 2006

**Highlights:**

The staff of the FEL Upgrade facility had a short week last week due to
the Thanksgiving break. However, prior to stopping operations on last
Wednesday, we collected two more days of data on short Rayleigh range
operation of the FEL. Recall that theory predicts and our initial
measurements confirm that the FELs will have an advantage in operating
at shorter Rayleigh ranges-which would allow the FEL beam to diverge
faster enabling the design of shorter optical cavities for a given power
limit on the mirror.  The timing of these data was excellent because
this week Steve Benson presented the results at a review of this project
at JTO headquarters on Tuesday, followed by discussions on the topic
with visitors from the Naval Postgraduate School, yesterday and today.\
\
This week FEL operations were devoted to several user experiments or
preliminary tests\
as described in the User Operations Section below. The Univ. of Md team
continued their development of a unique electron beam diagnostic using
the FEL linac, the Cornell team continued their development of a THz
interferometer, and the joint Yale University/Hampton University team
started engineering tests of their experiment designed to search for a
dark matter candidate particle.

**Management:**

We completed the project financial reports for October 2006 and
forwarded them to the DOE and ONR program offices. We continued
preparation for the next visit of a contingent from ONR for a briefing
and status report on FEL achievements and plans.\
\
We were pleased to welcome Professor Joe Blau and four students from NPS
this week to discuss continuing our collaboration on theoretical
modeling of the JLab FEL performance.\
\
Hui Tian presented a paper at the recent AVS meeting on surface studies
of niobium for SRF accelerators co-authored with her advisors, Michael
Kelley and Charles Reece, and university collaborators.  Michael Kelley
presented a paper at the recent Materials Research Society meeting on
antimicrobial surfaces.

**User Operations:**

This has been a busy week for user operations with 3 users taking beam
and 1 user setting up.

1.  Mike Holloway and Anatoly Shkvarunets from U. MD continued their
    experiments on Optical Transition Radiation Interference, which aim
    to elucidate electron beam emittance properties by measuring the
    spatial coherence of the light emitted as transition radiation.

2.  Nick Agladze from Cornell University used THz light to investigate
    the performance of a novel interferometer without moving parts, that
    utilizes an array detector to stare at an interferogram of the
    entire spectrum.  This will be invaluable as a pump-probe dynamics
    tool, as it multiplexes the data collection while offering
    considerable immunity to intensity fluctuations.  It also has
    potential use as a machine diagnostic tool, capable of video-frame
    rate images representing the electron bunch length in both pulsed
    and cw operation.

3.  Most of the week was spent setting up for the first engineering run
    for the Light Pseudoscalar or Scalar particle Search (LIPSS), a
    collaboration of Hampton University, Jefferson Lab and Yale
    University. The main purpose of this engineering run is to identify
    anything not working per the LIPSS requirements, prior to an
    extensive run early next year. We were able to get the dipole
    magnets fully powered, boundary regions roped off, equipment aligned
    and cameras mounted and working. Background data were recorded to
    determine the behavior of the LIPSS detector in the magnetic fringe
    field, RF when electron beam is running in the vault, and with NO
    FEL light into the system. System checkout with FEL light will occur
    at a later date.

4.  Mike Smith (NASA Langley) and Kevin Jordan prepared and qualified a
    new high pressure sample chamber that will extend the capabilities
    of the nanotube work to allow BN samples to be studied.

In all this work we benefited enormously from help from our Safety
Division.  It is imperative to do careful work planning prior to any lab
activities.  Among other things, this planning includes a task hazard
analysis, waste stream analysis and the development of mitigation
procedures as necessary.  We work closely with our users to identify
hazards and to develop safe operating procedures.  We thank our safety
staff for carefully checking these documents as well as ensuring their
implementation.

**Beam Physics (Mike Holloway):**

I was able to get beam images and far field interference patterns with
the beam focused to horizontal and vertical minimums. From these images
I can determine the rms beam sizes (OTR beam image) and divergences (far
field interference pattern). I can then use this information to
calculate the x and y rms emmittance.  I have images using two different
narrow band filters .I will use the two sets of data for comparison. 
Also, I will see if it is possible to separate out beam halo information
if there is indeed a \"halo\".

  The next step in development will be to use a translatable optical
mask at the beam image plane. Doing this, we can possible measure the
localized divergence as a function of position and construct a phase
space map. I have a beam image and interference pattern with a profile
plot for illustration. Results will be available as soon as I finish.

**WBS 4 (Injector):**

The photocathode has delivered 500 Coulombs and 96 hours of beam time
without a re-cesiation since November 1, 2006, the last time we
activated the GaAs wafer into a photocathode. With 3.6 W SHG from the
drive laser, the polarizer setup is at 60% for full charge. The record
delivered charge without re-cesiation is 541 Coulombs in 47 hours of
beam time. The delivered charge could have been more but it was cut
short when the QE was obliterated by an arc on October 31, 2006.\
\
Another electrode coated with the field emission suppression film by W&M
has been mounted in the high voltage test stand. Previous results show
an outstanding performance with less than 3 pA (the noise level in the
measuring system) at 30 MV/m. The highest gradient in the photocathode
gun electrodes is 12.5 MV/m at 500 kV.\
\
We performed an experiment in a test vacuum chamber to find the
threshold temperature for arsenic loss from the GaAs wafer during the
heat cleaning process. Arsenic loss causes the surface roughness to
increase leading to scattered light. Presumably the scatter light causes
beam halo as the wafer is heat cleaned several times during its
lifetime. We did not observe any increase in the scatter light with CCD
camera as the wafer was heating up because the mount expanded and the
laser light was blocked by the tantalum cup holding the wafer. However,
after re-steering the HeNe laser it was clear that the scattered light
had increased significantly. We have modified the setup to have a better
angle of incidence on the wafer, have added an RGS with electron
multiplier to monitor Arsenic, and have made arrangements to use a
photo-multiplier tube for more sensitive measurements. We also
calibrated our wafer heater using a calibrated pyrometer. The soaking
temperature on the wafer is 545 C +/- 5C when the wafer heater
thermocouple readout is 670C.

Gun HVPS - Fully operational without any failures or trips.

**WBS 6 (RF):**

RF - The RF system was fully operational for this week\'s Users.  Only 2
cavities in zone 3 had to be adjusted slightly to make them more stable
under pulsed conditions.  The Injector Phase Monitoring system was
deactivated this week to test and solve a GPIB problem with other
systems.  It will be reactivated next week.  A search for a more
temperature stable RF mixer is ongoing for the Injector Phase Monitoring
system.\
\
**WBS 8 (Instrumentation):**

Installation of the magnet box supply for the LIPSS experiment in User
Lab 1 was completed this week, thanks to EES for resetting the taps for
this load. Line phase voltages were tested along with all the internal
interlocks exclusive to the supply.  External power leads, LCW and
thermal sensors were tested and passed for function. A number of
diagnostics were added to the line to ensure ease of alignment.

The Drive Laser Pulse Control (DLPC) System was updated this week to
provide a method of controlling the pulse mask that is used when the
pulse width changes. The feature was deemed necessary at a time when we
were concerned about the pulse width transitions in single shot mode.\
  It is not clear yet whether we will need it for single-shot mode,
however, we can now disable it for standard operations. Effectively,
this improves the usability of the M55 system. Recent trouble with the
M55 system was the motivation for making this change.  In the process of
diagnosing trouble in the M55 phase transfer function system revealed an
I/O conflict in the GPIB control system. To solve this problem we have
decided to separate the GPIB control loop into two. The work is
scheduled to happen on Monday and we are preparing for the work.
Additional rack clean-up and cable labeling is being prepared as well.\
In helping with the LIPSS experiment, the analog voltage from the FEL
light power meter was connected to EPICS via a spare ADC channel in the
control room. Time was also spent exploring how Fourier and Wavelet
methods can be used to solve the ADC noise in the LIPSS image file.\
   As the December down approaches, we are involved in a good deal of
work planning and preparation. The first batch of cables for the
expanded FEL timing system has been documented as well as various cables
requested by the optics group. An updated time line of the FEL programs
milestones over the years is being prepared for the end of the year.\
Designed mechanism for a filter flipper bracket to remotely extend and
retract.  Fabricated arm component of the mechanism, and the machine
shop will be fabricating the cam wheel by 12/05/06.\
Created CAD drawings of camera box panels and delivered to the machine
shop for fabrication.\
  The Queued Serial Peripheral Interface Module was programmed on the
Coldfire processor, which communicated with the General purpose board.
Work began on writing the code for the new Vacuum control board.\
 Work began on an x-y axis configuration for BPM calibration using
several Aerotech linear stages; one of the stages is wired and ready to
go, the other is waiting on some tech support from the company.\
  The 15W power supplies ordered from Astrodyne were received this week,
and the stepper driver box for the sputtering chamber was finished this
week.\
  The 74.85 FEL Drive Laser chassis was finished and delivered to Tomasz
Plawski. He is waiting for a few filters to arrive so testing can begin.
The Single Board IOC Module is being populated as parts arrive.

**WBS 9 (Beam Transport ):**

Improvements and Upgrades

• With regard to SF sextupole, Neil Wilson, Head of the installation
crew, is trying to fit disassembly and reassembly before a second test
to see if magnet fields repeat and to mimic the vault's cramped
conditions.   

•  Facilities Management continues working on raising the capacity of
that Drive Laser Room's cooling unit, a task that will enhance our
ability to keep the drive laser phases stable.

•  Concerning work on the second wiggler chamber, we ordered the flanges
and windows necessary clean it and to flash a copper coating to the
inside.  We are still about to solder on cooling tubes.

• In work for the New Gun and injector Test Stand, McAllister Technical
Services hasn't come back with their final design of the proposed
device. Riggins Co. still has the tank for the high Voltage Power Supply
to bring it back to operable condition with a "hydro" test.  With regard
to vacuum bake-out of the new gun chamber, we haven't had time to
restart this effort.  The order is placed 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.  Ron Lassiter completed the final drawings of the apparatus that
will allow remote withdrawal of the cathode stack for cesiation without
opening the gun tank.

Experimental program

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

• The LIPSS Group brought the apparatus up to full working condition. 
Magnets were brought to full field, with fringe field at the 0.5 mT
level (pacemaker limit) extending out to about one meter from the
magnets in all directions.  Alignment Folks checked alignment of the
pole positions of the generator magnets and regenerator magnets, finding
that they were co-linear within tolerance.  Stands for Optics were
installed, filled with sand for vibration damping and grouted in place. 
The experimental plan for the Engineering Run was started on Friday. 

**WBS 11 (Optics):**

During the week of the Thanksgiving holiday we assisted in measurements
for the JTO-funded Short Raleigh Range experiments.  We found that our
technique of using the size of the retro-reflections of the mirrors on
the wiggler viewers gave values consistent with those measured by other
means to within 2 cm (out of \~ 16 m).  This is also the level of
uncertainty in the ROC determination by our two other techniques (test
plates and the Wyko laser interferometer with a calibration standard). 
We began lasing on the new 1.06 micron mirror set mentioned several
weeks ago, but it is too soon to judge their performance. 

 

Michelle Shinn and Steve Benson gave presentations to a JTO panel in
Albuquerque for follow-on funding for projects on the second generation
deformable mirror design and Short Rayleigh Range studies.  Afterwards
we toured labs at the University of New Mexico run by Prof. W. Rudolph. 
Professor Rudolph and his group have ONR funding to study nonlinear
effects in coatings used for FEL mirror coatings.  We had a productive
discussion about upcoming experiments.

We supported the LIPSS experiment this week by bonding optics to cooling
plates, diagnostic installation and mirror alignment. This week was also
spent on preparing User Lab 4 for the Aerospace/LMES run scheduled for
next week. A mockup of the 14kW cryocooled OC mirror was setup in User
Lab 2 for the Navy tours.

Lab Transport /OTS

Assembly of the OTS hardware continued this week. All of the Brewster
window shrouds have been built along with all of the Harmonic Blocking
filters. Two of the Harmonic blocking filters are completely assembled
and ready to go while two still need actual filters in them, one of
which needs a helical coupling to be complete. There are a total of 2
complete user shutters built and two that are incomplete, one needing a
helical fitting and another also needing a helical fitting and support
rods for the air cylinder. More parts were picked up from the machine
shop to assemble the lab cans and I&C has been contacted about building
more beam viewer boxes for controlling the air cylinders.

Advanced Drive Laser

We focused our work on the optimization of the beam mode at each
amplification stage to resolve the distortion we found last week. The
temperature controller for the SHG was malfunctioning and prevented us
from getting the expected conversion efficiency. After the SHG power was
restored, we conducted a GaAs wafer heating experiment with ADL output
beam. High temperature was observed at different power level. This is an
important study for high current gun.  We held a short meeting to
discuss the phase resolution issues with the RF driver and a decision
has been made to modify the original design in order to reach the
required precision and stability. An EPICS control system is in
progress.

**Terahertz:**

For most of this week, we have been working with Nick Agladze from
Cornell in the THz lab to perform tests on a very clever interferometer
that he has designed and built.  The interferometer has no moving parts
save for the beam shutters and produces the interferogram from a single
pulse.  Because of this, it is capable of measuring the THz spectrum at
any repetition rate and duty factor provided there is sufficient power
for the detector array.  We have been able to determine some of the
limitations of the detector array currently being used.  We have also
been able to improve the THz beam optics into the instrument to increase
the span of the interferogram.  The spectral resolution of the
instrument depends in part on the span of the interferogram, so it is
important that it fills the entire detector array.  There are still some
problems with the measurement of the phase information that we will
continue to work on during beam operations for the LIPPS group today,
but we have had good results from these tests this week.  This design
should prove to be an invaluable tool for accelerator diagnostics.
Today, we will also be testing an electro-optic sampling system that
Nick built.  We have previously performed tests on this system and so
will be repeating those measurements to test some modifications that
Nick has made.\
\
Also this week, Matthew Coppinger, one of our THz imaging collaborators
from the University of Delaware, was able to complete some processing on
one of the THz imaging tests earlier in November.  He was able to
successfully reduce much of the background in the images and will
continue to work on other THz images and refine the processing
procedure.\
\
It should also be noted that the beam operations this week have been
excellent for the THz work.  During the THz imaging tests in November
with the Kolodzey group, we were able to achieve a very good alignment
of the THz beamline optics.  This was only possible with the improved
THz imaging capabilities provided by their camera system.  This week, we
were able to restore an accelerator setup to match that used for the
imaging tests, which brought the THz beam into near perfect alignment
with the hutch alignment laser used for setting up all of the optical
systems in the lab.  This greatly improved our ability to create tests
that are reliable and repeatable.