**MEMORANDUM**

**To:** Distribution

**From:** F. Dylla

**Subject:** FEL Upgrade Project Weekly Brief -- March 21-25, 2005

**Date:** March 25, 2005

**Highlights:**

This week was another extremely busy week as we time-shared between the
ERL Workshop held on-site and the activities in the FEL vault to
change-out the rf windows in the FEL-3 cryomodule. Both activities went
well.

As of this afternoon we are pleased to report that we successfully
changed out 3 rf windows on the FEL-3 module and the cavity assembly
within the module has been returned to ultra high vacuum levels (\~10-9
torr) in preparation for cool-down early next week. We plan on rf
testing of the module late next week which would provide the true
measure of the success of this venture. We note that the portable
clean-room that was designed and installed around the module attained
Class 10 conditions (which exceed the standards in our production clean
rooms). Also the heated, clean nitrogen purge gas system which we
designed for venting the module during the window change-out and
subsequent clean-up after window replacement appeared to work well. The
entire operation has gone according to plan to date and we thank the SRF
team for their competent execution.

The Energy Recovered Linac (ERL) Workshop held from last Friday until
this Wednesday provided a unique forum for over 150 attendees to discuss
all aspects of ERL design, construction, application and application.
The milestone demonstrations of the IR Demo and FEL Upgrade were
recognized as precursors for the increasing world-wide activities based
on this technology. We were pleased to see that engineering activities
are proceeding at both the Cornell and Daresbury ERLs that are providing
supporting information back to our projects. The full workshop
proceedings will note the array of on-going and proposed new devices and
include summaries of the working groups on injectors, transport systems,
hardware (rf, cryo,etc) and diagnostics. You will note additional
remarks about the ERL workshop from the system manager reports given
below.

Highlights of other activities this week include:

\- a visit by the Dahlgren group for initial set-up of their laser
materials damage experiment

\- progress on the assembly of one of the Turning Mirror Cassette
assemblies for the "full-up" Optical Transport System

\- completion of the design of the sextupole magnets for the UV FEL

\- excellent progress on the IR PM wiggler motion and vacuum systems

\- assembly of the (long-awaited) "multi-slit" diagnostic which will be
installed in the injector line for beam emittance measurements

**Management:**

We used the ERL workshop to advantage to engage with useful discussions
with many of our collaborators and vendors who attended.

Initial preparations were made for display material and tour logistics
for the Jefferson Lab Open House which will open up the FEL Facility to
the general public on April 16^th^.

Gwyn Williams attended the American Physical Society meeting in Los
Angeles, the largest physics meeting in the world.  He co-chaired with
Alan Todd (AES) a special focus session on Applications of THz
Radiation, which was well attended. Larry Carr (from BNL) presented the
JLab facility in his overview talk on high power sources. Gwyn also met
with Mark Sherwin and Mike Martin to talk about the National THz Science
and Technology network of which Mark is head.

**WBS 4 (Injector):**

We participated in the ERL Workshop this week with two presentations and
plenty of discussion on cathodes and DC Gun technologies.\
\
We supported Cornell activities on testing one of their electrodes in
the High Voltage Test Chamber.\
\
Work continued this week setting up the clean area in our new lab in the
ARC building.\
\
We hosted a meeting with Dr. Kiangyang Lu from Peking University on High
Voltage DC Photocathode Guns. Dr. Lu has a hybrid DC gun SRF injector
under construction in Peking and attended the ERL Workshop.

**WBS 5 (SRF):**

This week the SRF design team got a chance to measure ourselves against
the competition, so to speak, at the first international ERL workshop,
held at JLab. We presented our high-current cryomodule concept in public
for the first time (our FEL technical reviewers had seen some of the
work before but for many it was new). We also showed the latest
calculations on expected HOM damping for various cavity shapes and
damping methods. The material was well received and there was lively
discussion in all of the working group sessions. The conveners accepted
our findings that it was possible to achieve good HOM damping and
accelerating mode efficiency at the same time, and included this in the
working group summary. They also took note of our warning that HOM power
handling is at least as important as BBU threshold when optimizing these
structures. Of all the designs presented ours showed the highest packing
factor and potential real-estate gradient. There was also healthy debate
about power couplers, especially topical at the moment, with opinion
split between coaxial vs waveguide couplers. Since we are pursuing
high-power variants of both types, based on proven SNS and B-factory
technology respectively, we should be in a good position to select the
best choice when the time comes.\
    The ERL workshop aside we have converged on two waveguide end group
options that we wish to test, one with four damping waveguides on each
end, as previously shown to the review committee, and another with
three. The three waveguide option seems to give just about as good HOM
damping as the four-pack (better for some dipole modes), with simpler
mechanical layout and less static heat leak. We plan to make copper
models of each type to measure on existing copper cavity models. We are
still comparing cavity cell profiles to try to find the optimum balance
of HOM frequencies, Q\'s and power dissipation. Once we find a good
compromise we will go ahead and model that profile as well.\
    All told the ERL workshop was a great success, with our own programs
featuring prominently in all working groups (and not just because we
were the hosts!). Not long ago the debate was whether high-current
FEL\'s were even feasible, now they are using our machine as a benchmark
to show that they are not only possible but practical and affordable.

**WBS 8 (Instrumentation):**

This week began with our participation in the ERL workshop. One of the
many insightful meetings that took place provided us the opportunity to
learn about new accelerator modeling tools that are available,
specifically one which has been used to model \'our\' JLab FEL. Dave
Sagen at LNS/Cornell, in working with our CASA group, has recreated our
DiMAD model of the IR-FEL with his \'extensible\' BMad tool-kit and
generated what he has called, \"FELV\". In short, this tool takes in
difference orbit data and then solves the FEL transport model for all of
the quadrupole values. To date, we do not have an ops tool to do this,
and so we have been excitedly discussing how we can implement this tool
into our FEL ops use. Three immediate tasks have been identified. 1) We
need to get the existing FELV model running on our system and reproduce
the results that Dave Sagen\'s model does on his system, 2) we need to
update the FELV machine description file to match the latest machine
configuration (this is being addressed by Chris Tennant) and 3) we need
a script which will translate the results of our \'difference orbit
data\' into a data set that can be supplied to the FELV/BMAD model. Full
documentation on the FELV/BMAD tools is available from the following
link: <http://laser.jlab.org/devlore/devlore.asp?Item=6714>\
 The epics2devlore RF Fault Archiver is still in the process of being
tested.  The functionality of the system was tested successfully.  The
problem arises with the EPICS channels being used to monitor the state
of the RF system only providing fault coverage for the P1 machine
faults.  This is not an adequate trigger for viewing all the RF faults
that were requested to be monitored.  Through discussing the issue with
J. Coleman, G. Lahti, and Al Grippo the RF Zones 2, 3, 4 now have a
solution to this problem.  Zone 1 being the oddball is currently being
hashed out.  Zone 1 should be completed by close of business today.  A
final test run of the RF Fault Archiver system will occur during the
beginning of next week, well before we are expected to power on the RF
system for checkout. This week the DSP readings for the CTD CAN bus
chassis system were slowed back down so that more tests could be run.
The voltage mis-readings from the system were tested. It was discovered
that the voltage being displayed on EPICS was the same voltage going
into the DSP ADC channels A0 and A1, which is correct; however, the
voltages themselves were not what should be expected. The CTD boards
were pulled from the chassis and tested for correct mux and FPGA
operation.\
   Further testing was performed on the two RF-DC Linear Converter PCB
prototypes.  Tests to examine their response to RF pulses of different
durations as well as output response through an RF Switch were
performed.  These data will provide calibration points for pulsed beam,
CW beam, and multi-pass beam operations.  These tests are also providing
the specifications for the 4 Channel Filter PCBs and the RF-DC Linear
Converter Carrier PCBs.  The Optical Dump Multiplexer installation has
been completed.  All of the cables have been installed, terminated, and
checked out OK.  Some software changes were made to ensure that the
correct logic was implemented to match the EPICS screen.  The OCR
Optical Dump local flow controller was modified to allow remote control
through the Proportional Valve Control Chassis.  The cabling was
installed and verified.  A vendor was found that carries the grades of
phosphorous powders used for Beam Viewer target coating, 500 grams of
both grades were ordered for coating of future Beam Viewer targets.
Design of a 4 Channel Solenoid Fail-safe Interlock board for the new
Multislit is complete.  A prototype has been built and tested for proof
of principle. Rack fabrication and installation began for the Cold
Cathode gauges and controls to support zone 3 cryomodule testing. HV and
signal cable have been installed for the 4 controllers.  Installation
was completed in the control room for the new beauty frame and new flat
screen monitors. Assembly of the new multislits destined for 0F04 are
underway. All parts have been UHV cleaned and delivered to T. Day.

**WBS 9 (Beam Transport):**

***Sextupole (SF)***

• Fabrication is continuing at New England Techni-Coil. Core parts
remain in machining, aiming to get them all rough machined to go to the
heat treat in one batch the end of next week. Coil winding form and mold
are in manufacture.  Conductor was received.

***Replacement Chicane Dipoles GW)***

•   Fabrication is continuing at New England Techni-Coil.  Steel core
pieces for the second set of two dipoles are being machined. The coil
mold is being reworked by NETC to be more precise for their first coil
potting.

### UV Line 

• The first trial of a QX Quadrupole with a "Bang-Bang" hysteresis loop
on the test stand showed a 1% greater strength with harmonics remaining
the same as original tests.  The slow, linear ramp generator was also
tested but needs some work.  First indications are that the strength
changes, but harmonics remain the same.

•  Tim Whitlatch continues vacuum modeling.

•  The ME design group continues layout and documentation of the entire
UV branch (less the chicane). They continue the designs of the four
stand and girder types that we don't have.

•  The first fabrication release was made for the UV Stand/Girder System
as the twenty, post style stands were ordered through the Jlab Shop
fabrication system.

•  The next priority item to sign off is the stand placement points so
that the Survey and alignment folks can start laying out the stand
positions.     

•  Advanced Energy Systems has made great strides in designing the
stands and chambers for the GW chicane.  The stands are almost fully
detailed and the layout of the first of four chambers is nearly
complete.

### UV Wiggler Progress 

• We redesigned the viewers for the UV Chamber to have camera and viewer
mounted on the robust, plenum side of the chamber. Greatly simplifying
the chamber fabrication and eliminating high-risk welds in the thin part
of the chamber.  By weeks end, we signed off the revision A of the
drawings and transmitted them to Argonne National Lab.

### IR Upgrade Multislit for the Injector 

•   Tony Day of the Accelerator instrument group assembled the new
design Multislit and we surveyed it so that we will be able to install
it and align it by the end of the shut down, next Wednesday evening. The
Multislit will be able to measure transverse emittance at the exit of
the injector's Quarter cryomodule.

**WBS 10 (Wigglers):**

Efforts continue to provide information to the vendor for the wiggler
gap mechanism contract, including the details for the motor controller
panel and the support design.  Most of the action items from the
kick-off review have been completed at this point.  A new action item
arose in the last week when the vendor found that they had not designed
the lifting points as strong as called out in the specification.  The
design was revised to increase the strength of the lifting points.  The
rails and motors are now ordered.\
Our contact at Argonne National Lab suggested a design change that would
significantly ease construction of the UV wiggler vacuum chamber.  The
problem is making a port on the narrow side of the chamber.  This is
very difficult in an aluminum chamber.  Instead we will have both the
camera assembly and the viewer actuator on the same side of the vacuum
chamber.  This side has the plenum chamber on it so that connections can
be made very easily.  We have are modifying the chamber concept drawing
and the stay clear drawing to indicate this change and will send out
changes next week.  We sent out a request for information to the vendors
replying to questions from one of the vendors.

**WBS 11 (Optics):**

***FEL mirrors:\
***Metrology continues on the new transport mirrors. Our first set of
measurements show that the new elliptical transport mirrors appear to be
passing spec uncoated, but are failing when coated. We will test the
rest and get back to the vendor.

***Other activities:***

The outgas rate study setup is checked out and is being baked for the
first time (the resulting aroma caused everyone to stay clear of User
Lab 1). Measurements begin next week. Work continued on the first
turning mirror cassette. Work in the vault for the streak camera
transport from the first arc is essentially complete. The prototype OBPM
is in fabrication. Michelle and Shukui attended the ERL Workshop.
Michelle met with staff visiting from Peking University, and explained
some of the details of the current drive laser system. We assisted staff
from NSWC Dahlgren, who were here to set up their hardware.

***UV FEL***

The design team is implementing our suggestions from last week\'s design
meeting. The conceptual design for the optical region between the
outcoupler and the collimator was fleshed out.

**Terahertz:**

Meetings were held with Eric Grossman of NIST, Boulder, CO, Colin Baker,
Teraview, concerning imaging experiments in lab 3.