# MEMORANDUM 

**To:** Distribution

**From:** George R. Neil/gpw

**Subject:** FEL Upgrade Project Weekly Brief - February 26-March 2,
2007

**Date:** March 2, 2007

**Highlights:**

This week we continued machine operations delivering beam sustained
above kW levels for many hours at 1.6 microns.  These longer term tests
are extremely valuable in providing experience for prolonged operations,
with simultaneous steady power levels, and positional stability.  We
also ran at 935nm for extended shifts for the ONR funded LIPSS
experiment.\
\
Correction - for the record, last week\'s 10 degree off-crest number
should have been 20 degrees.  Thanks to those who noticed!

**Management:**

Steve Benson, Dave Douglas, Michelle Shinn, Bob Rimmer and Claus Rode
participated this week in the FEL Technical Area Working Group (TAWG)
meeting at Brookhaven National Lab.\
\
Steve Benson also visited the Source Development Lab at Brookhaven, and
the NISUS wiggler in particular.  He also looked at hardware
installations for the DOE nuclear physics ERL project, which will
provide electrons for cooling the Relativistic Heavy Ion Collider.\
\
Gwyn Williams represented Jefferson Lab at a Department of Energy, Basic
Energy Sciences Advisory Committee meeting in Bethesda this week, and
also gave a colloquium at Hampton University on Thursday.\
\
Mike Klopf and Gwyn Williams provided Alan Todd with material for the
quarterly THz program review which was on Thursday.

**Operations:**

The first string spent much of the week in Brookhaven at the
TAWG meeting so the second string took over and ran the machine
this week.  They managed quite well.  As is always the case when some
are put in charge, they learned quite a bit as well.\
Over the weekend we had another AC power fault, which dropped the clean
power for the FEL facility.  We are still exploring why this happens. 
The personnel on hand over the weekend were unable to bring the machine
back into operation due to some faults caused by the power cycle.  We
therefore spent part of Monday operations bringing the machine back into
a running state.  One injector RF control module had to be replaced and
this changes the phases in the injector so we started by re-phasing the
injector.  Once this was done we set up for high power operations at 1.6
microns.  This power was used for some metal cutting experiments in User
Lab 2 and nanotube studies in User Lab 1.  Once these experiments were
done we switched to 940 nm operation and started delivering beam for the
LIPSS experiment.   This continued for the remainder of the week.  The
machine ran stably all week.  We had no problem delivering 1 kW to both
the metal cutting and nanotube studies.  The 900 nm mirror losses
prevent us from delivering more than a few hundred watts to the LIPSS
experiment but it is quite stable and runs for many hours with only
occasional interventions to tweak the optical transport or electron beam
energy.

**WBS 4 (Injector):**

The photocathode gun delivered 153 Coulombs and 46 hours of CW beam time
for FEL ops during the week. The high voltage power supply tank was
grouted to the floor of the Gun Test Stand. Fabrication of the resistor
assembly for the gun test stand has started. Progress continues on the
final fabrication stage of the new gun chamber. Preparations are
underway to vacuum fire the gun chamber here in the lab, instead of
sending the chamber to an outside vacuum furnace. D. Bullard continued
working on coating the wiggler chamber.

 

Gun HVPS - It remains fully operational.

**WBS 6 (RF):**

RF - When the machine experienced a hard AC power crash this past
weekend, the RF system lost 1 low level RF Control Module out of 28
units.  A recently calibrated unit was installed, the RF parameters
downloaded, the machine was then aligned, and the system was operational
again.

 

The current trip level was increased for the faulting external circuit
breaker and all of the major individual circuit breakers were lowered to
about mid-capacity or less.  This was done to determine which, if any,
of the major power supplies is causing the problem.

 

By analyzing his data of the RF system, T. Powers was able to determine
the Probe cables for cavities 5 & 6 of zone 3 are the likely culprits of
minor energy jumps.  These cables will be checked and tightened at the
next vault access opportunity.  A linac energy signal was developed and
displayed on a strip tool screen, so a minor energy change is now easily
correctable by the operator.

**WBS 8 (Instrumentation):**

This week began recovering from the power outage last weekend. A meeting
was held with plant services and the electrical safety folks, here is
the details from Todd Kujawa (Electrical Safety): the instantaneous trip
setting on FEL-BKR-414 was changed from 1.5 (3,000 AIC) to 10 (20,000
AIC) at the request of the FEL group and to be able to further
investigate the suspected nuisance tripping (most recent trip was this
past weekend). The breakers at PNL-FEL-ELEX were also set back to a
point just above halfway on the instantaneous setting. If the breaker
was already below this new set point then it was left with its original
setting. The expected scenario would be, (if there was a trip due to a
high inrush of current), that the trip would occur closer to the
equipment that caused the trip instead of at FEL-BKR-414. The end result
would be to have FEL-BKR-414 coordinated correctly with PNL-FEL-ELEX. 
This setting change at FEL-BKR-414 now has a direct effect of how the
LTT process is carried out with PNL-FEL-ELEX since the hazard energy
level, with the new setting at FEL-BKR-414, is beyond a level of PPE to
protect against while performing voltage verification. The new process
will be as follows for LTT of PNL-FEL-ELEX:\
1) turn FEL-BKR-414 instantaneous setting from 10 to 1.5\
2) lockout/tagout FEL-BKR-414\
3) proceed with normal LTT procedures for PNL-FEL-ELEX while wearing the
PPE required for a Cat 1 hazard at an energy level of 2.4 cal/cm^2^.\
4) After work has been completed and FEL-BKR-414 has been re-energized
then change its instantaneous setting from 1.5 back to 10 and verify
this setting has been saved.\
    I (Todd) have talked to the JLAB electricians about this and
facilites management is also aware of this procedure. I (Todd) will
place a notice on PNL-FEL-ELEX as a reminder to this procedure. I (Todd)
have also talked to the JLAB electricians about installing a VVU on
PNL-BKR-414 when the FEL goes down in a few weeks. The VVU would
eliminate the need for this extra procedural step when performing LTT on
PNL-FEL-ELEX. - MANY thanks to Todd for this help.\
    We have begun setting up a new development information server,
specifically, we are setting up a JLab Computer Center Maintained Apache
server which will be the future location of the configuration control
database and devlore content. The machine name will be  \"fel.jlab.org\"
and will also host a wiki of the same build as the now famous Wikipedia
website (namely, the \"mediawiki platform). This is motivated by the
over-due need to move-away from the FEL maintained Microsoft Server
platform (with IIS, ASP and MS Access database back-end) which currently
runs the site at: \"laser.jlab.org\". Over the next few months, the
existing devlore web-interface will be made obsolete and the
functionality of devlore will be provided through the new FEL \"Wiki\"
and related server applications.\
    The opportunity to test the new AMS/Video software has been
scheduled for this coming Tuesday owl shift. Even though that is next
week we have been continuing to refine it to ensure its success. Also
this week, the operational status of the Laser Personnel Safety Systems
EPICS data being archived by devlore will be added to the FEL status
page at the top of the log book. The graph will provide the last 8 hours
of system status.\
    Activities in User Lab 5 began with a re-organization of equipment
in order to make room for M. Kelley\'s JTO collaboration. Fabrication of
the User Lab status panels have been completed and tested.  The panels
will be installed as time allows.\
    The user runs have forced the staff to become proficient in the many
systems required for FEL operations; this experience is invaluable for
cross training and for the staff to better understand current operations
and how to improve/streamline ops for the future!

**WBS 11 (Optics):**

***FEL Mirror Development***

The majority of this week was occupied with my trip and participation in
the FEL TAWG meeting at Brookhaven.  I presented a talk on the path to
higher average power FELs that was well-received.  The TAWG was also an
excellent opportunity to meet with Al Ogloza (China Lake) and Carmen
Menoni (Colo. State U.), members of the Optics Improvement
Collaboration.  Al brought some very useful information, obtained with
Stanford\'s photothermal deflection technique, that shows microscopic
regions of high absorption on an otherwise ultralow loss background. 
Identifying the source of these regions, probably due to some process
parameter during coating, and eliminating them will be important in the
quest to achieve even higher laser damage thresholds than observed now.

***Optics Support***

This week we supported three user experiments in both setup and FEL
operation. The week started with finding the 1.6um OC mirror's pitch
motor some 0.3 radians off its aligned position. We are not sure what
caused this dramatic pitch change but we suspect it was due to the
weekend power outage and subsequent partial restore of the IOCs.  Monday
after re-aligned the 1.6um cavity, we configured Lab 2 for the laser
cutting of stainless steel experiment. We closely supported this
experiment by providing a dedicated professional optics group person to
assist in sample setup, alignment, stage and shutter control, and in
experimental direction during the 16 hour shift.     

***Cavity/Transport Optics***

We have finally had time to complete the drawing for the remaining
cavity and transport scatter absorbing shields. The drawings are
currently in the machine shop for fabrication. We anticipate machining
of the molybdenum 3" OC rings for the High-Q cavity cryo-mirrors to be
completed next week. Today we will submit a purchase requisition for
eight additional 3" deformable HR mirror assemblies. A micro controller
and temperature sensors was ordered for the Optical Beam Position
Monitor (OBPM). The controller has multiple PWM/timer capabilities. It
has been decided that the OBPM wires will only need to be in the beam
path for the duration of a measurement request so a timeout is being
included in the software. This should eliminate the overheat problems,
but a temperature monitor will be included in the software. Preliminary
EPICS control requirements for the OBPM chassis interface have been made
to the software group.

***Laser Work***

We did not get the time to work on the advanced drive laser this week
due to other work and the available time in Lab 6. Except for one
special custom optical assembly, all the parts needed for the Gun Test
Stand drive laser phase compensation system are ion the purchase
requisition system. We did an initial check on the Ti:sapphire lasers
and are in the process of optimization and characterization them.
A preliminary plan was made for setting up the laser system for the EO
sampling experiment. Our calculation has provided final parameter for
the EO sensors. The setup is ready for measuring the response of FEL to
modulation of electron bunches. The Antares drive laser is operating
normally but the power started to drop with increased current. We will
replace the lamps on the nearest possible chance. We helped our Japanese
user in setting up the laser-material interaction test and continued to
help ODU with the upcoming experiment in Lab 6.

**Terahertz:**

Much of this week was dedicated to preparations for our presentation at
the March APS meeting next week as well as assisting Alan Todd prepare
for the quarterly review of the Advanced Energy Systems THz Systems
Development program on which we share a collaboration.  The reviews
seemed positive, and we hope that the imaging results that we have had
so far will help to garner more support for this program.  We will
continue to push the THz imaging study, and this week, we received one
of the lenses that we expect will improve the performance of our imaging
system.  We have another type of lens on order that is not expected to
be completed for another 2-3 weeks.  Once we have both lenses, we hope
to schedule another THz imaging run and see what improvements we can
make.\
\
Wade Brock, also took data this week for his study on the THz beam
polarization.  We had to make some modifications to the setup that was
originally planned, but after that, we were able to perform a full set
of measurements to check that our system had sufficient dynamic range.
We also checked the beam alignment and tested all of the data
acquisition systems.  We have not completed the full set of data yet,
but the initial results appear to reveal some interesting spatial
dependence on the polarization across the beam profile.  We think this
can be understood due to the mixture of radially and linearly polarized
emission due to edge radiation and synchrotron radiation respectively.
Data collection will continue today.\
\
Also this week, the vacuum FTIR spectrometer was reconfigured and setup
to properly interface and align to all of the vacuum systems, the
optical table, and the THz beam path after having been removed for some
time.  Once the reference laser was realigned to the interferometer, the
spectrometer was brought back to life and we are currently running tests
on the system.  One problem that was found was that one of the globar
sources used for characterizing and testing the system has failed and
will need to be replaced.  We are using a spare globar for now, and can
continue working on the spectrometer.

**Users:**

This week we ran 3 user groups.  1.  Eisuke Minehara from JAEA, Japan,
is a world expert on high power laser-metal interactions. \"In the
Stainless steel machining, we were able to use excellent light beam
parameters of 0.5-1mmmrad in alignment mode or low power operation, and
good parameters of 2-3 mmmrad or larger in high power mode at 1.6
microns.  Four rods of 6mm diameter, 4 pipes of 10mm diameter and 0.5mm
thickness, several plates of 5mm thickness, and a nuclear fuel length
dummy were used as targets for cutting and drilling.  4 cubes of 10 mm
steel with milling marks were exposed to ablate these machining marks.
In the very beginning, a couple of rods could be cut reasonably and
sharply and welded again instantly.  The FEL power in User Lab #2 was
varied between 200W and 1.1kW in Hutch mode.  All of the samples are to
be measured and examined by standard material tests and inspections
later.\"  2.  Mike Smith, NASA-Langley writes \"NASA is eagerly
analyzing samples acquired this week in a new nanoparticle synthesis
chamber. Because of the high average power and stability of the FEL, the
researchers were able to quickly move through a matrix of over 30
chamber/laser conditions in a single shift.  Some preliminary results
show exceptional promise which we hope to confirm and report on
shortly.\"  3.  LIPSS, the ONR funded LIght Pseudo or Scalar particle
Search, completed 19 hours of operations at 935nm with the light
polarization parallel to the magnetic field.