# MEMORANDUM 

**To:** Distribution

**From:** George R. Neil

**Subject:** FEL Upgrade Project Weekly Brief -- April 9-13, 2007

**Date:** April 13, 2007

**Highlights:**

As a final test before shutting down to install the High Q Optical Test
components, we were successful in energy recovering high charge (270pC)
at the longitudinal brightness required for an FEL amplifier (80
keV-ps).  Injection energy was only 5.5 MeV. Hardware installation of
the cryomirror test components proceeded well; by Thursday all the high
reflector components were installed and beginning pumpdown. The
outcoupler components are being installed today.   The wiggler chamber
coating was completed and preparations are underway for installation
beginning Monday.   Substantial gun test stand efforts are also in
progress.

 

After five years as the Associate Director of JLab\'s Accelerator
Division, Swapan Chattopadhyay will soon begin a prestigious appointment
as the Sir John Cockcroft Chair of Physics, the Inaugural Director of
The Cockcroft Institute and a principal member of the steering
committees for the flagship \"fourth generation\" light source, 4GLS,
which is now in preparation at the Daresbury Science and Innovation
Campus in the UK.   We wish him good fortune in this exciting work and
look forward to the collaborations which will allow us continuing
benefit from his wisdom.

**Management:**

Planning within JLab is focused on developing a loading plan for
personnel to support the ONR/NAVSEA Program while meeting JLab
engineering needs for the 12 GeV Upgrade effort.

We held a meeting to review Technology Transfer at JLab and the
management of that activity.  Under consideration is to make the
management of that effort formally incorporated in the business
management of the lab.

We held a scheduling and planning meeting for the gun test stand
activities.  Procurement of a gun tank appears to be critical path due
to requirements under new DOE pressure vessel regulations. 

**100 kW Design Periodical:**

Chris Tennant reviewed and reported on physics issues for the 100 kW
system. Having performed an initial assessment of  BBU effects in
systems with off axis injection \[nonfatal\], he has moved on to
consideration of amplitude dependent effects in RF focusing. Chris and
Tom Powers continue work on the RF drive issues.\
\
Kevin Beard is setting up a PARMELA simulation of MADMAN-style systems
to cross-check preexisting out-of-house simulations of off-axis
acceleration with space charge. Results are forthcoming.\
\
We have generated a preliminary baseline layout and solution
\[\"BrightLight\*  \"\] for a relatively compact (20-ish m X 3 m) 100
MeV system that can be configured for either amplifier or oscillator
FELs and allows modest transverse and longitudinal tuning in either
application. Injection is at 5 MeV, extraction at 4 MeV, with complete
energy recovery. Recirculator acceptance is appropriate to a 1%
extraction efficiency, and (by migrating to incomplete energy recovery)
likely to be scalable to higher efficiencies. Given the community\'s
general faintness of heart about transforming the sow\'s ear of RF
focusing into a silk purse via direct injection, traditional merger
geometries are assumed.\
\
We are discussing how to carry forward the present phalanx of 100 kW
driver designs {baseline BrightLight, \[3 injection energies\] x MADMAN}
x {amplifier, oscillator}. Complete nervous collapse seems to be the
designer\'s preferred approach to date.

# CSR data analysis:

# Due to the shutdown time this week we got some time to analyze the data of the CSR experiments we did the last two weeks. Some development of the numerical algorithms was necessary and has been done. We have analyzed in detail the bunch length measurements made with the Happek device. We have also started to analyze the electron beam energy spectra data. The first iteration of the data analysis has shown that more accurate analysis of this part of the data is required. However it gave us confidence that we have made very sensitive measurements of the electron beam energy spectrum change. We continue to work on the data analysis.

**Machine Ops/Beam Physics:**

This week\'s single day of operation was devoted to pushing bunch charge
and lowering injection energy. We ran - for several hours - pulsed beam
at 270 pC/bunch from 5.5 MeV/c injection momentum to a full momentum of
around 110 MeV/c, and recovered it to 7 MeV/c. Beam quality was improved
beyond that in the last low-injection energy run (where we were unable
to progress past the wiggler), and we were able to demonstrate
compression of at least some portion of the charge to \~450 fsec fwhm.
Energy spread at \~110 MeV was around 1.5% full width. Emittance was not
characterized quantitatively, but the beam spots \"weren\'t too
horrible\".\
\
Further work is needed to improve beam quality and further reduce losses
before running high power. Guidance for this has been provided by
PARMELA simulations (which suggest relaxing the 2nd injector solenoid).
Injector steering was performed only roughly (simply to avoid vacuum
excursions in the front end); improvements in this area will likely be
both straightforward and profitable. We need to set the match of
recirculator excitation to energy more carefully, and tune up the energy
recovery longitudinal match (which was, at best, \"poorly optimized\").

**Injector:**

The DC photocathode gun provided 270pC bunch charge beam for beam
studies on Monday with cathode QE around 5%. Our ODU graduate student,
Deepesh Kumar, has made significant progress modeling the FEL injector
with 500kV gun. His results indicate that we might be over-focusing with
the second solenoid.\
***Gun Test Stand***\
We have identified the existing FEL drive laser Antares as the choice
for the GTS. It will need modifications to meet pulse energy specs for 1
nC bunch charge, but it should be able to provide 0.5 nC as is now with
a 5% QE photocathode. We also held an update meeting with installation
and I&C groups. New tasks and requirements for various systems were
identified.

Installation - The redundant copper piping has been removed and new
piping installation started, while nitrogen and air piping re-work is on
hold until next week.

**Instrumentation & Controls:**

The Gun Test Stand is again taking center stage. The AC power
connections for the new 75KVA transformer have been installed and the
transformer has arrived. It will be hung (from ceiling), connected to
the 42 slot panel and powered up next week. The thermocouple hardware
and software for gun bake out has been installed and is operational
(showing the room's poor temperature regulation). The PSS group has
begun to install their ductwork for the interlocks in the GTS. Locations
for the Run Safe boxes have been determined.  Since personnel are
working in the GTS vault they (PSS group) will extend the main FEL ODH
alarms (magenta beacon and horn) into the room first. The cable raceway
will be extended on the east end of the equipment floor to accommodate
other PSS interlocks. Five more equipment racks have also been ordered
for future installation of diagnostics, magnets and RF. The EPICS
workstation in the GTS control room is now operational. We are adding a
second monitor to this machine. The PC is also up and running. This will
be set with a remote (in the GTS vault) monitor and keyboard for data
collection. Monitors for the video system as well as USB-over-cat5
extenders are on order. The SF6 gas transfer design is progressing and
will be reviewed by the JLab pressure vessel experts (cryo group) next
week. The previous CAD drawings of the Gun Test Stand Vault have been
modified. Some of the assembly components had unresolved links but we
were able to resolve many of them. The newly run chilled water lines
have been incorporated into the 3-D CAD model. And finally the HVPS tank
has a bright shiny coat of Ferrari red paint and is ready for assembly.\
Further testing of the FEL shutdown script showed that some minor timing
adjustments needed to be made.  The changes were tested for the weekend
shutdown and only the controlled access needs to be tested.  The new
wiggler software failed to work properly on iocfel6.  So iocfelt2, the
test bed, was changed to contain the exact same hardware as iocfel6.
Debugging of the application is in progress. There was some code
modified for the connection between the ColdFire and FPGA for Single
Board IOC. Also more general purpose I/Opins are going to be connected
to allow the IOC have more configuration flexibility.  The EPICS code
for the Beam Viewer control application is being developed for use in
the FPGA.\
The driver laser pulse control system (DLPC) was improved this week by
modifying the system to provide a single, stable logic trigger to the
drive laser tek-scope. The previous configuration used a combination of
the Photodiode-signal (which is highly dependant on EO cell biasing) and
the vernier mode gate signal. That configuration is not completely
reliable and often required attention from the operator. Using a
wide-band, bi-polar COTS signal distribution amplifier (Phillips
Scientific Model 6950) we were able to free-up one of the 1vp logic
(analog outputs) pulses from the DLPC and use it as a maintenance free,
reliable trigger. The work was done as per the FEList Task (ID #100546)
and everything went smoothly as planned. The operational readiness of
the drive laser after this was confirmed by the Optics Group.\
Some effort was also spent this week working on the HVPS Control Crate
electronics for the GTS.  The SBIOC schematic modifications were all
completed and reviewed.  The layout modifications are in progress and
this board should be ready for order early next week.  The PCB layout of
the Analog Distribution Module is also progressing.  Initial thoughts
and design for the crate backplane began this week as well.\
    Some of the instrumentation for the High Q Mirror Cavity Test was
installed.  The required cabling was installed and terminated.  The
breakout crate is also installed with the diode crate.  The test fixture
is connected to the optics can side of the cable to simulate the
temperature diodes.  Once the ADC portion is ready we will take data on
the noise of the system.  This will give us a baseline resolution for
the required measurements.  An abstract was written for the 2007
ICALEPCS Conference.  This is currently being reviewed before
submission.\
Continued progress is being made this week in moving the configuration
control database functionality to the new FELWiki site at
[http:fel.jlab.org/wiki](). This week we were successful in installing
the mySQL ODBC driver on laser and configure it to provide a datasource
connection to the lab\'s jmysql database server where the new apache/php
based devlore tools will live. Currently, we are working to resolve
minor differences in the way that data is stored between the two
systems, this should be resolved soon, after which, we will be able to
update the FELWiki database with the information in the Devlore database
automatically until the FELWiki site handles the work itself. Also, an
effort is underway to add content to the FELWiki site. The following
pages are being worked on:\
\* An FEL Procedures Page where the FEL Start-up from Hot Stand-By
Procedure has been added:\
<https://fel.jlab.org/wiki/index.php/Procedures:FEL_Start-Up_from_Hot_Stand-By>\
\
\* An FEL Lessons Learned Page for non-notable event lessons learned in
FEL OPs,  Management and users runs:\
  <https://fel.jlab.org/wiki/index.php/FEL_Lessons_Learned>\
\
\* A page presenting all of the FEL-related \"JLab Notable Events and
Incident Investigations\" which have occurred since 1999:\
<https://fel.jlab.org/wiki/index.php/FEL_Notable_Events_and_Incident_Investigations>\
\
\* The New FEL Machine Pics and Photo-Gallery:\
 
<https://fel.jlab.org/wiki/index.php/Photo-Gallery_of_Machine_Pictures>\
\
In addition to working on uploading all of our existing procedures, we
are attempting to use FELWiki site as the official documentation
location for the Gun Test Stand (GTS) Project, but this is an experiment
and will certainly teach us a lot about how to use the wiki for
collaborating on project tasks and status.\
The GTS Project article is at:\
<https://fel.jlab.org/wiki/index.php/FEL_Gun_Test_Stand_Project_Overview>

**Electron Beam Transport:**

Improvements and Upgrades

*New Gun Test Stand*

• No work on this because of work on new wiggler chamber

> *SF Sextupole Magnet Testing*

• The Accelerator Division's Power Supply Group continues their
commissioning of the CANBUS control of the new power supplies.

*Cooled and less resistive Wiggler Chamber*

• Sputtering of the Chamber with copper started on Thursday and is
complete. We could not start the bake we anticipated for last weekend.
We attempted to assemble the complete electrode system into the chamber
last Saturday. We found the slugs that extend the shape of the chamber
beyond the ends needed to have their slot opened up. In addition a lip
on one side of the slug interfered with a gasket ID. Then the copper
electrode strip needed some additional pieces tacked to it. One of the
electrode feedthroughs needed to be lengthened. The shop was very
accommodating in responding to some simple part machining. In addition,
the SRF group tack welded the slugs to their flanges and the extra
pieces of copper to the electrode. We were finally able to button up the
assembly on Wednesday afternoon leak-free and clean. We baked at 150C
overnight, purged with argon and cooled the chamber down by Thursday at
noon. We reverse sputtered for about 16 minutes in the magnetic field.
We then initiated sputtering for two 4-hour runs each with a separate
half of the chamber exposed to the magnetic field. On Friday morning we
examined the depth of copper on four sample disks placed in the BPM
flange positions at the ends of the chamber. They measured 1.3 microns
which was within the desired tolerance.

• To accomplish the above sputtering in a manner consistent with our
highest safety practices; a considerable amount of effort was applied to
writing and perfecting the Temporary Operational Safety Procedure (TOSP)
for the task. We received great cooperation from the Safety Folks, Ned
Walker, Todd Kujawa and Patty Hunt to name a few. The TOSP was signed on
Wednesday.

• Jim Coleman provided great help in setting up our workspace in the
South Access Building to good electrical and safety practice. Neil
Wilson was greatly helpful in suggesting the South Access Building to
begin with and in grabbing and installing the magnet stand from the bone
yard and the magnet from the ARC Injector Lab.

• Just in case the above plan A was not successful; we established a
dialogue with a Pennsylvania plating shop that was recommended as having
the capability of plating the chamber.

# **High Power Optics Risk Reduction**

New measurements of the loss (determined from ringdown data) of the 900
nm mirror set as a function of wavelength were made with a faster (Si,
rather than InSB) detector.  The loss values are in general agreement
with data taken earlier in the month, and at odds with the data taken in
late January.  After some discussion, we believe the newer data is
probably more correct.

  The Optics Group opened up the OC vacuum vessel a bit early to allow
us time to introduce a standard lamp (a standard of spectral irradiance)
before the OC mirror.  This was used to calibrate the spectral response
of the hardware used to make measurements of the harmonic content, both
intra- and extra-cavity.  The calibration files are in the process of
being generated. 

  We have an experimental setup to test the efficacy of apodization as a
means of better controlling the light diffracted from various apertures
in the FEL optical systems.  Our first measurements, using an unapodized
disc, are in excellent agreement with the simulation from OPC (the open
source physical optics code created by staff at the Univ. of Twente, The
Netherlands).  Our plan is to use OPC to rapidly determine the best
apodization function for a particular situation.

  The test plan for the High Q optics test is in preparation.

  We received word today that the Colo. State Univ.-led optics
improvement proposal, entitled, \" Fundamental understanding of optical
coatings and novel strategies for power scaling of high power Free
Electron Lasers\" in response to an ONR BAA has been approved.  This
proposal provides funds for an expanded group of researchers in the US
to work on optics improvements.  It also provides funds for testing the
coatings and optics at JLab.

**Terahertz:**

In preparation for venting of the 4F region for the installation of the
new wiggler chamber, the THz beamline was vented as a safety measure for
the diamond window vacuum interface.  Also during the down, additional
outlets are being installed to improve the electrical safety condition
in the lab.  Most of the time during the first week of the down though
has been dedicated to completing a manuscript on the THz imaging work
performed with the University of Delaware group and assisting Wade Brock
prepare his senior thesis.