# MEMORANDUM 

**To:** Distribution

**From:** F. Dylla/grn

**Subject:** FEL Upgrade Project Weekly Brief - November 13-17, 2006

**Date:** November 17, 2006

**Highlights:**

During the first part of this week we removed the cryocooling from the
1.6 micron mirror and re-installed our standard water-cooled mirrors for
1, 1.2, 1.6 and 2.8 microns in the outcoupler can. (Note that our
current version of the cryocooling option does not allow multiple
mirrors to be accessed in the optical cavities). This return to our
standard configuration will allow us to continue our FEL studies for JTO
and Navy programs over the next month and a half.  As discussed below in
the Operations section after re-establishing FEL operations, we
initiated detailed studies on short Rayleigh range operation.  These
tests will continue through next week.

We also held a successful design review for our 750 MHz 1 Amp
cryomodules project.  Although there are still some outstanding design
issues to resolve, overall the effort is in good shape to proceed with
element design engineering and component development tests. This design
review was a key deliverable in our Navy program plan for FY07

**Management:**

We prepared and submitted follow-on Phase II proposals for our current
JTO projects and completed our submission to SAIC for our contribution
to their follow-on.  Those proposals will be defended at the JTO office
in 1 1/2 weeks.

A coordination meeting for the Yale/Hampton University LIPPS experiment
(the axion search) was held this week to coordinate efforts for their
requested engineering and first data runs. The monthly teleconference
for our Biomedical Photonics Consortium was held today. Plans were
initiated for a 1-day workshop early in the new year to coordinate CY07
proposal development.

Preparations continued for on-site meetings with NAVSEA and ONR on
December 1 and 8. ONR distributed the final agenda for our Jan.17-18
annual review to the review panel.

Gwyn Williams presented an invited talk on how the JLab FEL maps into
the landscape of 4^th^ generation light sources, and Fred Dylla
presented an invited talk on the development of high voltage from Ben
Franklin to the International Linear Collider at this week's AVS
Symposium in San Francisco. Marcy Stutzman from the CEBAF Source group
presented a comprehensive review for the need for extreme high vacuum in
photoemission electron sources. Many of our FEL users attended this
meeting.

**Operations:**

This was a fairly short week since we spent much of the week pulling out
the cryomirror and putting the room temperature mirrors in place.  We
were able to lock up late Wednesday and check the injector drive laser
alignment and turn on RF.   We turned on Thursday morning at 2.8
microns, switched to 0.94 micron operation for JTO tests, and tuned up
the laser at that wavelength.  With the tuning almost done the CHL
tripped.  It took most of the day to pump down the CHL.   During this
time we calibrated some diagnostics for the JTO work.  We continue the
JTO studies of short Rayleigh range today.  The efforts today are to
carefully calibrate the Rayleigh range measurement using several
different techniques.

**WBS 4 (Injector):**

The photocathode lifetime is around 1667 Coulombs after adding up the
extracted charge from last Friday\'s run. So far the photocathode has
delivered 472 Coulombs since Nov. 1 without re-cesiation. With about
2.5% QE left, the Drive Laser polarizer is set at 40% for full charge.\
\
The operating vacuum conditions in the gun improved significantly after
the Helium was pumped out from the injector cryomodule during the
shutdown earlier this week.\
\
We have been studying the effect of soaking temperature on the GaAs
wafer surface morphology during the heat clean cycles for photocathode
activation. There is clear evidence from AFM data between a fresh GaAs
sample and a heat-cycled one that the temperature used so far is too
high and is causing As depletion and consequently increased surface
roughness. This increase in surface roughness leads to drive laser
scatter light that reflects off the mirror-finish anode plate and lands
on other areas of the photocathode outside the drive laser illuminated
spot. We suspect this scattered light is the cause of beam halo observed
as the photocathode undergoes increasing number of heat cycles. In a
preliminary test, the scattered light from the heat-treated sample is 20
times larger than that of a fresh sample, as measured by the CCD camera.
A simple experiment has been setup to find the threshold temperature for
the As depletion. We expect to get some results early next week. Then we
will make a photocathode using this threshold temperature to make sure
it is high enough to produce good QE.\
\
D. Bullard helped remove the wiggler cooling plates and made some more
progress polishing the molybdenum anode plate for the test stand gun.
Drawings for the motorized photocathode retractor system to be
incorporated to the FEL gun for reducing the FEL down time during
re-cesiation are being reviewed. The corona shield fabrication for this
new scheme was sent out for bid.

**WBS 8 (Instrumentation):**

The first part of this week was spent debugging and repairing a set of
embedded BPM electronics that Operations had noted as failing.  The
electronics were removed and after several series of tests it was found
that due to the on board regulators the board was over heating.  To
remove the heat and to dissipate some of the load on the regulators some
in series diodes were added to reduce the input voltage and also a fan
was installed to increase air flow.  This problem is being taken care of
on the next revision of the electronics.  In the process of testing the
electronics, we also replaced the ADC and recalibrated the electronics. 
The calibration code was uploaded and the electronics are working fine. 
Other down time activities included repairing SLM2F08 attenuators and
installing interlocks for the new windowed valve VBV1V01.  Various
cables were also installed since the risk of crashing the machine was
eliminated.  The PC felpx02 was repaired and reinstalled in the vault.

The upgrade for the Wiggler control software was tested.  The serial
communication to the Wiggler\'s Galil motor controller is not working
properly.  The IOC appears to be sending the commands properly, but the
Galil controller is not transmitting the values back to the IOC.  This
is currently being investigated.  The QSPI module on the Coldfire board
has been programmed, which will control the General purpose board.  We
programmed the FPGA code for the new version of Single board IOC.  The
second revision layout of the Single Board IOC Module is being
populated.

    Much time has also been spent this week getting together everything
that is needed for the Beam Viewer upgraded crate prototype.  We\'ve
verified the operation of the test box to be correct and are in the
process of testing the Control Cards.  Some tweaking of the PLD code on
the control cards has been done and some further tweaking remains.  The
assembly of one of the backplanes has been added to the queue since the
board arrived from the board house early this week.  Currently the
cabling to break the backpanel out and into the rear field connections
panel is being configured as well as the locations for the power
supplies.  The latest revision of the Single Board IOC has arrived and
the first one of these will begin testing today.  The plan is to use
this new revision with the 3U General Purpose I/O(GPI/O) card as the
processor for the prototype Beam Viewer crate.  The GPI/O has also been
added to the queue for assembly. We are waiting on parts to finish
populating the 3U General Purpose I/O card.

    We\'ve also taken the time to coordinate with the EES/DC group for
the sextupole power supply installation that will take place during the
next down.  We\'re currently acquiring the requested external ADCs
needed for their setup as well as getting the GPI/O tested for
installation in their crate.  To give them some time to fully test their
system into a load we\'ve began the installation of the reversing
switches onto the power supplies.  The water line manifold parts are all
in hand and these are partially assembled.  The other parts to provide
the switch cooling are being acquired.  A required modification to
externally interlock the switches to the power supplies is being planned
so that it can be implemented as soon as possible.

    Progress was made on the LiPPS experiment with the completion of the
power lead installation and connections.  Installation of the Klixon
wiring and water cooling hoses is in progress.  Planning is in progress
for \'safing\' the magnets and power supply which includes barriers,
flashing beacons and installing additional kill switches in the User
Lab.  Additional Beam viewer Interface boxes, PC boards and parts have
been ordered In support of the Optics group User Lab upgrades.\
    We are fabricating the 74.85 MHz chassis for the FEL Drive Laser. 
Assembled the computer numerically controlled milling machine.  In
support of the LPSS upgrade for labs 3A and 6 some cables were
installed.  Also some cables were installed to support lab user
operations.  Work was done on the driver box for the sputter chamber;
the box is complete except for a 12V power supply, which has been
ordered from Astrodyne and is due in the week after Thanksgiving.

    Rich Evans has spent the week in preparation for an oral defense
for his Masters Degree in Applied Physics at CNU.  The defense is today
at CNU and (if it goes well) will be the conclusion of his graduate
studies at CNU.

Work has been done on the calibration procedure of the log-amp base BPM
electronics. The proper calibration is one of the critical aspects of
this sort of the BPM electronics. First to speed up the calibration
procedure, while keeping it precise, a precise 1-to-4 RF splitter has
been assembled, calibrated and tested for long term stability. The goal
of the BPM electronics calibration is to collect data, which would be
sufficient to reconstruct the level of the input RF signal with the
accuracy of about 0.1 dBm or better by measuring the output DC voltage.
Therefore during the calibration the RF signal level at the input of the
electronics has to be knows with the accuracy better that the 0.1 dBm.
For the calibration we use an RF generator with the amplitude accuracy
better than that. To calibrate all four channels of the electronics
simultaneously it was desirable to have 1-to-4 RF splitter with the
difference in the attenuation from, channel to channel, much less than
the 0.1 dB. Commercially available splitters do not offer this level of
precision. By putting adjustable attenuators on the output of a 1-to-4
splitter we could adjust the difference in attenuation between the
different channels to be on the order of 0.01 dB or even better. As the
next step the long term stability of the combination of the calibration
RF generator and the splitter was measured. Driving the test we would
drive the splitter with the RF generator and measure the power level at
the output of the splitter with broad band RF power meter. That has been
done for a time span of about two weeks. The RF level at the output
would not change by more that 0.02 dB, which is a combined variation of
the RF generator the splitter and the power meter. Hence the variation
of the splitter itself is less that that and is very good level of
stability for the log-amp based BPM electronics calibration. Use of the
precise splitter reduces the time needed for the calibration of one set
of the electronics, which is about 1 1.5 hours, by a factor of 3 4.

We also made a transition to another RF generator to be used for the
calibration. For that reason the calibration software was rewritten to
use the new generator.

 **WBS 9 (Beam Transport ):**

*IR Machine Operations*

• We removed the temporary cooling plates on either side of the Wiggler
Beam Chamber to enable it to close its jaws to the full extent.  This
will bring back the large temperature excursion and deflection of the
tube at high beam currents.

*Improvements and Upgrades*

• With regard to SF sextupole, Neil Wilson's installation crew is not
able to perform a disassembly and reassembly to mimic the vault's
cramped conditions due to higher priority work. 

•  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 are still about to
solder on cooling tubes. We determined what to order for flashing a
copper coating to the inside.

•  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. With regard to the contract to Riggins Co. to bring the tank for
the high Voltage Power Supply back to operable condition with a "hydro"
test, the tank was delivered to them.  With regard to vacuum bake-out of
the new gun chamber, we haven't had time to restart this effort.  Larry
Munk has sent out the bid drawings 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 continues working on 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* (LIPPS)

•   The group was able to insert the new pole tips in the proper
location and mount the light tight regeneration tube in the second set
of GW dipoles. The stand for the Optical Dump is mounted and the
Refrigerator/Camera stand, the mounts for the water-cooled turning
mirrors and the remaining parts for magnet covers are being made by the
shop.  The GW magnets were wired up by the electricians and they then
disconnected and locked out the magnet until the covers can be put on
and the SOP written and signed off.  The group is planning for an early
December run.

**WBS 11 (Optics):**

As noted in the Operations section the first part of this week was
devoted to removing the cryomirror and associated hardware and
installing the standard water-cooled mirrors.  These are for operation
at 2.8, 1.6, 1.2 and 1.06 microns.  The 1.2 micron mirror will be used
in conjunction with the broadband HR mirror.  The new 1.06 micron OC
mirror is of a new coating design that should allow harmonic lasing at
355 nm as well.  This will dovetail neatly with determinations of the
accelerator\'s performance.  Operation at the fundamental will provide
more stable output for the upcoming, Navy-funded experiments by the
Aerospace Corp.  As noted last week, the installation of these mirrors
allows us the opportunity to push the 1.6 and 1.06 micron mirrors to
their limits after the THz traps were installed. A presentation to
receive JTO funding for the second generation deformable mirror design
was prepared.  It will be given later this month. 

We prepared several 1.06 micron mirrors to be shipped to the University
of New Mexico for measurements of nonlinear effects in the coatings,
especially for mirrors that had been used in the FEL vs a spare that had
not.

For the standard water cooled mirrors that were replaced on Monday,  two
of the mirrors are brazed and two are pasted.  By Tuesday these mirrors
were aligned and the output coupler vacuum can was purged overnight with
hot dry nitrogen.  On Wednesday, OC vacuum was slow to recover, likely
due to extensive component replacement and having the vacuum can open to
humid air for so long.  By Thursday, the FEL was lasing albeit with
unwanted mirror vibration.  Things improved when Dave reduced water flow
to the OC mirrors and turned OFF a vacuum turbo pump.

The modified EO cell/pulse picker for the advanced drive laser, with
rotated output polarizer, was reinstalled.  Aligning the EO cell and
verifying proper beam specifications downstream of the amplifier chain
and frequency doubler is the last \"optics\" step toward installing the
ADL at the FEL.  On other ADL related fronts, Al Grippo is using epics
to communicate with ADL electronics although some commands need more
work.  The RF group is constructing a 74.85MHz source for the ADL and we
anticipate delivery soon.

**Terahertz:**

For most of this week, Gwyn and I have been on travel.  Gwyn was
presenting at the American Vacuum Society Meeting.  I am up at the NSLS
at Brookhaven to perform far infrared spectroscopy measurements on
several materials of interest, repeat some of the noise measurements on
the NSLS light source with the new signal analyzer system that I have
built and coded, and to complete as much preliminary setup as possible
for the magneto-optical tests that we hope to schedule here for January.

# FSU Effort

FSU FEL.  We continued discussion to cover the merger region and
identified a proposed layout of the machine which is somewhat changed
from previous ideas but with advantages We held a review of the Parmela
modeling status of the injector and booster region of the in operational
flexibility and physics performance.  We will continue our analysis to
see if the design holds together under further scrutiny.

More PARMELA simulation were made of the injector of the under design
FSU FEL. A corrected RMS transverse emittance value was used in the
simulations. Deliverables of this set of simulations are the initial
beam condition for the beam line design downstream of the accelerating
module of the injector. Another set of simulations was carried out to
study the beam propagation through a merger. A copy of the present JLab
FEL merger was used in the simulations. This set of simulations shows
acceptable, from the point of view of beam compression in the merger,
phase energy correlation of the beam at the exit of the accelerating
module. We also had a brainstorm session to discuss the possible machine
layout and to determine next steps in the lattice design.