# MEMORANDUM 

**To:** Distribution

**From:** F. Dylla

**Subject:** FEL Upgrade Project Weekly Brief --July 26-30, 2004

**Date:** July 30, 2004

**Highlights:**

Today, ONR released a press announcement on the 10 kW milestone which
can be found on the ONR website: www.onr.navy.mil/media.

This is the last week of FEL operations before we shut down at 17:00hrs
today for a maintenance/installation break until September. Since
obtaining first lasing last June, we have spent 40 weeks of
commissioning effort to bring the machine up to the 10 kW milestone.

We devoted this week to several important pre-shut down tasks:

(1) We lased on a second "high reflector" optic at 6 microns which had
    its backplane coated with metal to test for lower absorption. We
    need more run time to see if there are any significant benefits to
    this change; however, it did demonstrate another 10 kW class optic
    from the same vendor chain.

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(1) We lased at 2.8 microns to generate light at this wavelength to do
    calorimetry on the 2.8 micron optics to quantify the absorption
    loss. These results are again helpful for our feedback to the optic
    manufacturers. At first look the absorption in the coatings on these
    optics appear to be a factor of two below our specification and we
    are returning them to the vendors.

(2) We pushed the operation of the new (3^rd^) FEL cryomodule to 80 MV
    with 2 mA of beam current. This is a new world's record for cw
    operation of an acceleration module.

(3) Finally, we took additional difference orbit data on the driver
    accelerator so that the present operational configuration can be
    more fully documented and analyzed.

**Management:**

Our ONR Program Manager spent a day and half with us early in the week
to review

Draft documentation for our FY05-07 ONR funded FEL activities. In
addition, we prepared for next week's visit by ONR's Scientific Advisor,
Dr. Steven Lubard.

We had additional meetings with the Engineering and Installation groups
to plan the activities for the August shut-down which include:
installation of the short wavelength (1-3 micron) electromagnetic
wiggler; design and fabrication of a small magnetic chicane to deflect
terahertz radiation from the downstream optic; and numerous minor
upgrades and fixes to the optical cavities and miscellaneous diagnostic
systems.

**WBS 4 (Injector):**

On Tuesday evening we had to do a cathode re-cesiation due to a gun
vacuum event. The gun vacuum started to rise as the voltage was being
increased after a gun HVPS trip which did not close the laser shutter
due a blown component in the HVPS controls. At around 50 kV, the
pressure rose to the 10E-8 Torr range. The low electric field in the gun
was not enough to focus the photoelectrons that desorbed gas from the
chamber walls, perturbing the 1E-11 Torr range gun ambient vacuum. Later
that night the problem in the HVPS controller was found and fixed.\
\
Despite the vacuum event, the cathode still had 2% QE left which led us
to try a re-cesiation. The QE increased to 4.8% with the re-cesiation
(number six on this cathode). The cathode had delivered only 34 Coulombs
before the event on Tuesday evening. The cathode was HV conditioned
without problems and ready for operations the next morning.

Gun HVPS - Operational.  Responding very well to pulse operations.

**WBS 6 (RF):**

All RF systems are operational.  Preliminary discussions were held this
week with an RF high power tube vendor on the follow-on projects for the
100 mA injector test stand.  Written specifications will be updated for
the major RF components of possible upgrades or new machines.  They are
used in design of the RF systems and produce good cost estimates.

**WBS 8 (Instrumentation):**

On Tuesday a failure in a radiation monitor caused the high voltage on
the gun to drop while we were running CW beam. Procedures were followed
while bringing systems back on but the hard drop of the gun HV blew out
an interlock in the gun high voltage chassis. This caused the brief
vacuum transient in the gun noted in the gun report. This occurred at
the end of the shift, so recesiation during second shift caused no loss
of beam time or performance. This event with the gun interlocks revealed
an error in the drive laser pulse control system\'s MPS interface
circuit. The error was the duty factor interlock circuit could be
defeated to allow CW running under certain conditions. Although the
system performed properly to detect a duty factor violation and would
always protect the machine from transitioning into a higher current beam
mode, the interlock-fault was not permanently latching and could be
cleared later by a user by pressing the \'reset\' button several times.
This has been corrected. In a way that was completely unrelated to any
activities since 1996, we had a limit switch failure on the ND2 filter
in the drive laser clean room. After the exact cause of the problem was
confirmed, the limit switch was replaced. It was very unusual timing for
a random failure of this kind.\
    Another timer card is being commissioned in FL03B10 from iocfel3.
This card will handle the multipass BPM RF-switch logic. A 37.425MHz
sync-signal has been run from the drive laser clean room to the card and
the more subtle aspects of the boards performance is being tested. This
card will divide down the 37.425MHz by 32 (to 1.169MHz) which is the
highest micropulse frequency that will still provide enough
time-separation of the 1st-pass and second pass beams. It takes \~433ns
for the 1st pass beam to travel around the machine and be seen again by
the same BPM. Since the period of the 1.169MHz micropulse frequency is
\~855ns, this works out perfectly to allow a 1.169MHz square ware signal
to be a gate signal that continuously separates the two beams. The timer
card will do the clock division and provide phase control to properly
adjust the timing of the system.

    Bids were submitted this week from various vendors in response to
the Request for Information (RFI) as well as the Statement of Work for
the LPSS PLC purchase. We look forward to working with these vendors to
bring to the FEL an improved LPSS system.  A MIFARE card reader/writer
and developer resource kit has been ordered from ADI. Work continued on
the THz hutch design for Lab 3A and revisions to the design were made
with final plans being approved and parts ordered through the machine
shop.  Documentation of the ITV and SLM interface boards and boxes
continued. Fabricated another SLM interface box and began preparing
assemblies for shutdown installation activities. Additional CCD\'s and
Power Interface Boards (PIB) were ordered for the maintenance period.
Effort continued on the AMS chassis; there are 6 that are near-
completed and will be installed during the down. The Stepper Motor
Chassis front panel pcb package was signed off and delivered to EECAD.

    Five Differential Pressure Transmitters have been sent to OMEGA for
repair.  This leaves us one spare until they are returned. Data entry
for inventory continues.  Most of the resistors in stock and about 1/2
of the Integrated Circuits have been logged and associated specification
sheets downloaded. Four circuit boards for the new revision to the Si
Diode Thermometer Board have been populated and are ready for testing.
Minor adjustments were made this week to the BCM schematic this week.
The new setup was reviewed and we are in the process of placing an order
for the boards to be made.  Work continues to get the multi-pass BPMs up
and running. Inventory data-entry continues, the database pointer system
continues to make progress and

preparation for the AMS/Video system upgrades continues. New filters are
being tested on the viewers this week. They are 40 & 80 nm wide HeNe
interference filters. They are used to block the electron ghost pulses.

**WBS 9 (Beam Transport):**

## Wiggler 

######## Electromagnetic Wiggler for 2.8µ 

• After some struggle with Hall probes, we were able to start
measurement in earnest. We found that a loop of the magnet lead from the
power supply was a source of a 5 Gauss field amplitude differences in
opposite adjacent poles at one end of the wiggler. After that cleared, a
1.5 Gauss difference, but opposite in sign at either end was changed to
half that value and reversed in sign by removing the mirror plates. This
led us to remove the field shunting tags on either side of the mirror
plate. We have these back from the shop, and measurements are
continuing.\
***Decompression Chicane to Reduce Downstream THz***

•   We can now start on a chicane chamber concept with a designer part
time.

• Robin Wines has found that the field integrals are within the
specification 2 parts in 10,000 at only 8 cm and out of spec at 4 parts
at the 10 cm. At this level of error, we will use shims on the inside of
the field clamps to bring the magnet within specification while on the
test stand.

• Magnet Enterprises International of Oakland shipped the remaining 18
required coils.

• At the higher price for cooling plates we are forced to go out for
bid. The contract for a 4-week delivery will be placed early next week.

• The shop has started making the parts to revamp the DW dipoles into
the EWs

• The strong back for the 2.8µ EM Wiggler is out for bid and the cover
is being detailed.

***Sextupole (SF)***

• Procurement on hold, pending 10 kW efforts

***UV Branch Line***

• We are working on a WBS costing of the remainder of the UV activity.

***Daresbury Collaboration***

• We had a productive session with three folks from Daresbury on
borrowing our equipment to be utilized on their prototype FEL.

**WBS 11 (Optics):**

**Plan A is to obtain low loss 6 um optics.  \
**Last Friday we installed another 6 um HR mirror that had the back
surface coated with tungsten.  We first tested it on Tuesday and it
appeared to be working better than the other mirror.  However, we need
more beam time and analysis to determine how much the absorbed heat load
has changed. Measurements were underway Friday during high power lasing.

 

**Our three Plan B\'s had the following progress:\
*Cryomirror:***\
We tested a 2 inch sapphire optic mounted in a conventional mount.  The
data is still being analyzed, but inspection of the fringe pattern while
the optic was under test showed no obvious deformation was occurring.

***2.8 micron mirrors: ***\
We did calorimetry on both an OC and a HR witness sample to assess
coating vendor performance.  The runs did not go as well as
anticipated.  The data is still being analyzed, and will be discussed in
next week\'s report.  More mirrors will be coated with a vendor of
known, lower loss coatings, and used when we start up in September.

***Scraper outcoupler:***\
No progress since the last report.

***Other activities:***\
Alongside supporting operations, we are preparing for the
shutdown/installation period.  For us, this means implementing
improvements to the optical cavity to absorb and dissipate heat from
scattered light, improve mirror mounting, and install an optical
transport system.  We spent time off-shift Wednesday to get ready
for calorimetry measurements, and found that so long as we do work for a
limited amount of time (in this case \< 1 hr), and through a small port,
we can recover sufficiently low pressure in the optics vacuum vessels to
begin operations within 12 hours.  On Tuesday we gave Q. Saulter, our
Program Officer, an overview tour of some of the JTO-funded work.  We
are taking advantage of Lt. Cmdr. James Thompson\'s 2-week Naval Reserve
tour of duty with us to put him to work on various topics of interest.

**Terahertz Project:**

Work concentrated on the mirrors and mirror mounts.  M2 and M4 did not
meet specifications for surface finish.  M2 & M4 were found to have
surface roughness of 68 and 100 nm rms roughness respectively, the
specification being 50 nm.  Since the specifications were easily met for
M1, the vendor asked that the mirrors be returned for re-working and
they were shipped back.  Meanwhile the plane mirror M3 is at Brookhaven
for inspection this week.  Some re-working of the M2 mirror support to
enable stronger springs to be attached was done this week.