# MEMORANDUM 

**To:** Distribution

**From:** F. Dylla

**Subject:** FEL Upgrade Project Weekly Brief -- November 8-12, 2004

**Date:** November 12, 2004

**Highlights:**

We continue to make progress toward re-establishing high power lasing at
short wavelengths:

    - we established a good injector setup and verified a procedure for
checking and re-establishing performance on a daily basis

    -we established recirculated beam in the with good orbits to the
dump; matching of the transverse beam is reasonably good up to the
wiggler

    -we briefly ran CW beam to verify low losses

    -we began characterizing beam transport in the new wiggler

    -as we performed operational checks several minor issues were
uncovered including wiring issues with the 2nd arc and wiggler trim
magnets (short and polarity problem, respectively), and a vacuum
interlock problem with the optical transport line which inadvertently
let the beamline up to dry nitrogen.  These systems issues will be
resolved by mid next week and we will finalize the orbit setup for
lasing. 

We also continued out preparations for bringing high power beam upstairs
by completing that portion of the Optical Transport System.

During a second shift activity, a new low level RF system designed by
collaborators at Cornell University was successfully tested without
beam. The system shows a much faster time response than the original
CEBAF system. Beam tests will follow

**Management:**

We released the August and September UV Monthly Reports.

Carlos Hernandez-Garcia and Robert Rimmer participated in the High
Average Brightness Workshop at UCLA.

We have been working the action items from our meeting last week with
AES on the plan for the cryounit assembly and Injector Test Stand
construction and tests.

December 8 and 9 has been chosen for a Project Status Review of our THz
program with Army Night Vision Laboratory.

**Commissioning (Steve Benson):**

On Friday we performed quadrupole centering in the machine and found a
good orbit.  The design match was reasonable and, with the THz chicane
powered, low loss transport to the dump was possible.\
Monday was spent certifying the personnel safety system (this keeps
people out of the vault during machine operations), and the Laser
Personnel Safety System for the optical control room (this keeps all but
FEL Operators out of the optics control room during laser operations).
Both systems passed their certifications.\
Tuesday was devoted to matching the beam around the machine and doing an
initial test of the emittance software recently developed by Nobuyuki
Nishimori, visiting from JAERI.  The first data indicated a few problems
that need to be ironed out but also was consistent with a 10 mm-mrad
emittance.  The match was completed up to the optical chicane.  The
shunt in this chicane was not working so it did not make sense to match
beyond that point.\
Wednesday, with the optical chicane shunt repaired, the match was
completed through the rest of the machine.  A problem was discovered
with the path-length magnets.  It was found that the second arc steered
when the path length corrector was changed and a very large change in
the path length supply was necessary to set the path length. This was
due to two problems, one a wiring problem, one an internal short in one
of the four coils.  With the THz chicane off it was possible to get a
decent longitudinal match and cleanly energy recover the beam.  The beam
was run CW for a brief run.  The beam loss monitoring system must be
re-calibrated before running significant amounts of CW beam.  Wiggler
commissioning with beam we then started.  The DC field compensation
field was set and it was found that the trim coils at either end of the
wiggler were wired backwards.  We reversed them and were set to test out
the new configuration when we had a vacuum incident that shut us down
for the rest of the day.  That evening we determined that the first
cryomodule and the cryounit would have to be warmed up to get rid of
nitrogen gas frozen onto the cavities.  We are using the time while we
get the cryomodule and cryounit temperature-cycled and pumped down to
verify vacuum interlocking, establish proper field polarities in the
arcs and wiggler trims, repair the shorted path length coil and finalize
procedures for several activities.  We expect to restart commissioning
on Wednesday next week.\
Evenings this week were spent very profitably testing a new RF control
system being developed at Cornell.  The tests were very successful and
will be reported more fully in the RF section.

**WBS 4 (Injector):**

The gun continued to provide beam for FEL ops this week. We observe
improved cathode lifetime. The present cathode QE is around 4%.\
\
Continued to polish the ball cathode and support tube electrode for the
second gun assembly.\
\
Two successful implant runs have been completed on a test tube in the
William and Mary\'s plasma-source ion-implant chamber. This test tube is
being implanted with a field emission suppression coating. After
completing three implant runs, the tube will be mounted and tested in
the high voltage test stand (this is a small, dedicated chamber with a
high voltage power supply capable of delivering up to 125 kV) at 25 MV/m
(the highest gradient in the gun support tube is 12.5 mV/m at 500 kV
operations). In this new implant mode and at this lower pressure (1
mtorr instead of 4 mtorr), the plasma barely enters into the sidearm. 
Plasma entering the side arm used to cause instabilities that led to
arcing when nucleation of SiO~2~ occurred at higher pressures. Thus, the
coating doesn\'t extend as far onto the tube as the previous runs even
though the tube is roughly at the same location in the chamber.  We
estimate that the thickness of the coating is \~0.28 - 0.3 μm thick
after 7 hours (according to the color chart).  Even though the coating
is thinner, we were successful.  No arcs.  No SiON dust (a little
ambient dust falls on the tube when the chamber is opened). The
procedure is 3.5 hours in the plasma (no GDC since the floating
potential is roughly 35V),  then 0.5 hours at 2.5-3 kV, followed by 3
hours at 5 kV. \
\
Carlos Hernandez chaired the \"Materials, Fabrication and Integrations
Group\" at the High Average Power and High Brightness Beams Workshop
organized by UCLA. The Workshop opened with plenary talks by R. Nguyen
(USN), D. Sutter (DOE), D. Nguyen (LANL), J. Rosenzweig (UCLA), J.
Lewellen (ANL), and S. Biedron (ANL)
(<http://home.physics.ucla.edu/calendar/conferences/powerworkshop/>).\
Two other working groups focused on diagnostics and injector
design/modeling. D. Nguyen from Los Alamos summarized the status,
projections and challenges of the three present technologies towards
high average power injectors, DC+SRF booster (JLAB 10 kW Upgrade IR FEL
Injector and JLAB+AES injector), Normal Conducting RF (Los Alamos) and
SRF Guns (ELBE). The JLAB 10 kW Upgrade IR FEL Injector, being the only
present technology to demonstrate high average current operation at 9 mA
CW. Issues at projected high average currents at the 100 mA level and
beyond were also addressed during the Workshop like transverse halo
control, measurement, and modeling, cathode heating by the drive laser
at the 1 Amp average current regime, RF power handling, etc. Major
challenges like cathode R&D (new concepts, materials, robustness, QE,
etc.), drive laser R&D (average power, time structure and pulse
shaping), and thermal management (in RF guns) were also extensively
discussed.

Gun HVPS - This equipment is ready for operations.

**WBS 6 (RF):**

RF - A vacuum event this week put dry nitrogen gas into the Quarter
cryounit and the cryomodule FL02 and as a result they are not able to
make any voltage gradient without a degassing to \~200K. Vacuum
interlocks and a fastvalve downstream of the linac protected FL03 and
FL04 from getting this gas also.  Additional fast valves are being
ordered to better protect the Quarter and FL02 upstream of the linac.

 

The Quarter and FL02 are being warmed-up to 200K this weekend to remove
the frozen nitrogen gas and they will be cooled back down to 4K on
Monday and 2°K on Tuesday.  RF testing is scheduled for Wednesday.

 

Preliminary testing of a new low level RF system was done this week by
Cornell and JLab.  The results were promising with this system able to
turn-on and tune the cavity to a 12MV gradient in 8 ms.  Our existing
low level RF system takes many minutes to establish full gradient.

**WBS 8 (Instrumentation):**

Progress continues on the Multi-pass BPM (MPBPM) configuration. Our
initial testing last week showed us that we have one addition
requirement in timing that was not addressed in the set-up. Although the
1 MHz signal is phase locked to the 37.425 MHz signal, it was still
jumping around with respect to beam sync. To solve this problem, we have
implemented another programmable timer card in IOCFEL03. Trying to
implement all of the systems timing signals with just one card was good
exercise, as we have designed them to do some pretty fancy tricks, and
we have never really played with the card in this manner. It is clear
now that we need one timer card to generate a \'beam-sync triggered\'
burst of 1.17MHz which is then delayed to match the BPM pulses.
Implementing another timer card was straight-forward but took a few days
to get everything right. Currently, we are cabling the system together.
A software issue that was discovered during testing caused unneeded
features.  This was repaired by Al Grippo and both sets of software
controls were tested and verified.\
    After having some difficulties with beam profile measurements
produced by the WesCam, a bug was found in the software and easily
fixed.  The results following the change provided users with the correct
data they needed and scaled the calculations to mm according to the
calibrations setup last week.  The Photocathode Gun Coulomb Archiver
underwent changes in its EPICS channel access after creating a very slow
memory leak on IOCFEL10.  The IOC has been monitored extensively and its
memory resources have stabilized after the correction to the Coulomb
Archiver.  The new Laser Personnel Safety System was demonstrated and is
being fine tuned for testing to begin next week.  The logic for correct
communication with the PLC user lab door locks is being tested.  The
documentation/manual for the new LPSS is on-going.\
    DEVLORE FLOG READER
([http://laser.jlab.org](http://laser.jlab.org/)) - In lieu of all of
the recent activities, and the increase in use of the system by the
whole group, we have identified some of the strengths and weaknesses of
the configuration control database and what our daily needs are for a
system like this. To this end, we are preparing an update to the system
that will better present the daily difference between the current status
and the ideal status of the machines configurations.\
    The *complete* OPTICAL CAVITY system diagram is nearly complete.
With the continued input from the optics team, we have completed a
\'working\' requirements document for all of the instrumentation and
controls required to operate the optical cavity and optical transport
systems that are not explicitly covered by any other major accelerator
system (i.e. the vacuum system). This document mostly consists of the
stepper motors, thermocouples, and water flow instrumentation as well as
the various hooks into the beam viewer systems and the LPSS. Additional
RTD\'s were also installed for the re-located upstream and downstream
OCMMS Cross.\
    Assembly continued on the UV Beam viewer frames with the internal
mirrors being assembled and mounted to the frames.   Certification of
the LPSS Master was completed this week.  Progress continued on the new
User Lab LPSS.  The first enclosure and PLC will be used as a test bed
for programming and testing. The GPIB controls for the Analog Monitoring
System (AMS)scopes have been implemented. Testing is in progress.

    The floating GC power supply regulator design is now complete, the
schematics are being updated and PCBs will be produced. An additional GC
Magnet Control Chassis is being fabricated by the EES Group and should
be in hand for testing early next week. Design drawings for the Beam
Current Monitor upgraded circuit board went back to EECAD for final
revision and new boards will be in house soon for populating and
testing.  Testing continues on the Optical Mirror Heater Control
Chassis.  This chassis should be available for installation early next
week.  The 32:32 Video/AMS Crosspoint circuit boards, populated by FSI
Systems, have been received and are being inspected and tested. 
Assembly and Wiring diagrams for the AMS Chassis are being reviewed. 
The Video chassis are very similar and assembly of the chassis for the
video upgrade will be beginning very soon.\
    Additional training was held on the Lab\'s Electrical Safety Policy
following the incident at SLAC.  This training further emphasized the
procedures to use when testing electrical/electronic equipment and
clarified some work definitions.  Posters have been made to be posted in
areas where electrical/electronic testing is performed to serve as a
ready reminder for technicians performing this function.  An additional
portable tool/extension test cabinet has been received and is being
installed.  Training will be held early next week on the use of this
extremely helpful device.

**WBS 9 (Beam Transport):**

***Sextupole (SF)***

• Procurement package is out to vendors for bid.

***Replacement Chicane Dipoles GW)***

• Procurement package is out to vendors for bid.

***UV Line***

• David Douglas issued the latest DIMAD for the UV Line. It is being
laid out to check for interferences.

• We have identified 18 girders from the IR Demo that we can use for the
UV Line. We have a modification drawing that converts the original QG
quadrupole girder to the larger QX girder.

***Variable Jaw Mechanism for the Permanent Magnet IR Wiggler (W55)***

• The Engineering Group is refining the reference drawings and a
keep-out-zone drawing that will be part of the Specification for the
procurement of the mechanism.

***Operations***

• We discovered that the upper left coil of the four path length
corrector coils (GG coils) built into the pole edges is internally
shorted. At this writing, we are trying to remove the short without
having to open up the magnet. It may take months to get another coil
made. David Douglas says we may be able to use just the path length
correctors of the first arc as a fall-back method of adjusting path
length.

**WBS 10 (Wiggler):**

The specification for the variable gap permanent magnet wiggler was
completed and sent to the potential vendor for comments and a cost
estimate.  We are now awaiting comments from that vendor before placing
the order.

**WBS 11 (Optics):**

***2.8 and 1.06 micron mirrors:\
***No changes since last week\'s report.  Procurement of the 1.06 micron
mirrors is holding to schedule.  After the vacuum event described below,
we used the alignment HeNe to check the OC mirror surfaces for dust and
they appear to be fine.

 

***Other activities:***\
We spent the first part of the week readying for the LPSS certification
in the OCR, and then we completed the OTS Lite configuration by
installing the diagnostics mirror (a silver-plated Si mirror with a
small hole in the center).  Pump down tests were scheduled when a vacuum
event occurred.  Given the incomplete condition of the OTS, valves, ion
pumps, and interlocks were not in proper states and we dumped the
majority of the dry nitrogen atmosphere (\~ 390 liters) into the
accelerator.  A review of all vacuum interlocks on both the FEL and OTS
systems is in progress. We have split the remaining time this week
between checks of the OTS, review of procedures, and alignment of the
matching optics into the optical diagnostics.  So far we continue to be
pleased with the performance of the OTS as evidenced by the alignment
HeNe. 

Progress continues on the new optical diagnostics.  Parts were received
to complete the fast scanning autocorrelator.  The LabView program for
the PbSe array has been modified to make it more robust.  The program
will run on a mini-ITX computer mounted under the optical table in the
OCR.

The drive laser continues to be a workhorse (hope this doesn\'t jinx it)
but our cavity length optimization routing needs an input from the
autocorrelator to make this happen.  I&C is working on providing this.

We held a videoconference with our first off-site user group from
Dahlgren and generated a list of action items.

**Terahertz Project:**

This week we hosted Oleg Chubar and the team developed code to calculate
integrated power loading from 0.1 to 10 THz, and its distribution on a
screen.  In addition we set up the code to work with beams of much lower
energy, down to 1 MeV, so that we can investigate optimal transportable
sources in the tens of watts range.