**MEMORANDUM**

**To:** Distribution

**From:** F. Dylla

**Subject:** FEL Upgrade Project Weekly Brief -- May 23-27, 2005

**Date:** May 27, 2005

**Highlights:**

A good fraction of the JLab FEL team attended this week's 4^th^ Navy
sponsored FEL Workshop hosted by Northrop Grumman Newport News. We were
pleased to see that the workshop was well attended by a useful mixture
of Navy, national lab, industry and university attendees. We presented
an update on JLab FEL activities and detailed talks

on gun/injector design, high current cryomodules, optics and cryogenic
issues. On Monday evening we gave a tour of the FEL facility to 50 of
the workshop attendees.

During the workshop, we were pleased to turn over the "B-Team" who
proved they had

the makings of graduating to "A-Team" status by bringing the machine
back-on line for high power lasing at 2.8 microns.

As discussed in more detail in the "Operations Section" below, with the
newly installed high power 2.8 micron optics, we are getting our first
look at the effects of eliminating astigmatism on FEL performance
-lowering the astigmatism error from 0.3 waves to 0.05 waves essentially
recovers ideal performance- and our first look at the effects of
short-Rayleigh range operation- it helps as predicted by Bill Colson and
his colleagues at NPS. With only a little effort devoted to improving
the electron beam match to the wiggler (which was started today and will
continue next week), the lasing efficiency has already improved to \~1kW
per mA.

Optimization at this wavelength (2.8) will continue before we stop for a
2-3 day period to install the high power 1.6 micron optics.

The program for the June 7-8, 2005 "Laser Bioscience Workshop" we are
co-hosting with Harvard, UVA and EVMS is complete and posted on the
workshop website:

[www.jlab.org/intralab/calendar/archive05/LBC/](http://www.jlab.org/intralab/calendar/archive05/LBC/).

Next week on June 2-3 SURA is hosting a THz workshop at SURA
headquarters in Washington, D. C. See
[www.sura.org](http://www.sura.org/) for details.

**Management:**

As noted above we devoted three days to the Navy FEL workshop and look
forward to the draft conclusions and recommendations for the Navy's plan
for high power FEL development.

We continue to work with Engineering, Operations and the SRF Institute
to coordinate the interleaving of UV installation activities, cryomodule
conditioning and swap-out with operation of the FEL over the summer.

Two temporary (40'x40') buildings were installed across from the FEL
Facility this week

to allow our I&C, RF and optics support teams to vacate the user labs
for start-up of user operations.

Final preparations are in process for the June 7-8, 2005 Laser
Bioscience Workshop. A full two days of presentations have been
submitted from the pool of \~50 registrants.

**Operations:**

Since most of the most experienced operators were busy at the MW
workshop from Monday through Wednesday, the machine was run by the
\"B-Team\" on those days.  They did well, getting the laser up and
running each day and demonstrating up to 700 W/mA with the configuration
provided by Dave last week.  They got the alignment mode system
re-certified with new allowed time structures and did some work on
meshing the multipass BPM electronics into the existing BPM system. 
They also did some alignment on the new streak camera line from the
first 180 degree bend.  We had some problems with the drive laser that
slowed us down on Monday and some phase drifts but otherwise things went
smoothly.  By Wednesday we had demonstrated that the machine could run
high current beam and lased well.\
On Thursday we tried to optimize the laser as best as possible with the
available match.  The match is not very good through the machine, and
the bunch is not very short but the laser still lases reasonably well. 
We found that the laser lased increasingly well as the Rayleigh range
was shortened.  This is the first time we have tried this with a
spherical high reflector.  Before there was a clear maximum and the mode
would start clipping in one axis before the other.  Now the beam starts
to clip uniformly over the full circumference of the mirror as the
Rayleigh range is shortened.  The gain, as indicated by the cavity
length detuning curve, did not change much as the Rayleigh range was
shortened and the efficiency increased with decreasing Rayleigh range. 
This is in qualitative agreement with Colson\'s simulations of short
Rayleigh range operation.  We cannot shorten the Rayleigh range lower
than about 20% of the wiggler length at 2.8 microns but the laser is
improving up to this limit.  The mode is not much more stable than one
expects however and small vibrations in the output coupler angle wiggle
the mode.  We will try to address this on Tuesday.  We will try to get
more quantitative data today and next week.\
The good news of all of this for high power is that, despite a rather
poor match and a long microbunch, the power output was over 1 kW/mA. 
The efficiency predicted is close to what is predicted in simulations
and rather high considering a large fraction of the beam is not
participating in the interaction.

**WBS 4 (Injector):**

The DC photocathode gun is operational, delivering electron beam for FEL
ops with 80% request on the drive laser polarizer. We plan to perform a
cathode re-cesiation on Tuesday next week.\
\
The second of three tube segments that will support the ball cathode in
the new gun stack assembly is being polished. The first segment was
finished last week at 1 micron surface finish.\
\
Drawings incorporating the replacement of the spacer ring with increased
length in the vacuum chamber and end flanges have been revised and are
almost ready for sign off.\
\
PARMELA work continued this week with the development of a simple
program to calculate emittances from the six-dimensional phase space
generated for each particle by Los Alamos version of PARMELA. We need
this information to compare our results with AES\' 100 mA injector
model.

**WBS 5 (SRF):**

> End can interface connection drawings are complete and ready for
> review and sign off for the 750 MHz injector unit. Remaining parts
> will be ordered once the drawings are signed off.
>
> All cavities have completed bulk chemistry and heat treatment
> processes and are ready for VTA testing. Flange seals are on site and
> VTA testing of the first cavity will commence next week.
>
> Layout drawings will be developed for the un-shielded bellows for the
> upstream (next to gun) section and for the "cookie cutter" shielded
> bellows for the down stream section. These layouts will then be
> incorporated into the overall layout drawing.
>
> A lot of progress has been made on creating a working model of the 100
> mA cryounit and interface with the injector gun. The AES cryounit
> drawing has been incorporated with JLab end cans and gun stand. The
> next area for development is the warm-to-cold beampipe sections. The
> beamline height for the FEL gun and injector unit is 42", while the
> beamline height for the remainder of the machine is 27" from the
> floor.

**WBS 8 (Instrumentation):**

The majority of the week was devoted to operations support.  J. Coleman
and Wes Moore (formerly the 'B' Team, now the A prime Team) maintained
machine conditions to allow testing of the Alignment Mode, alignment of
the Streak camera, and multipass BPM testing.  This is likened to Dad
being out of town (Navy FEL Workshop) and leaving the keys to the
Porsche. Their success in running did allow for a full week of testing
and preparation of FEL systems.  They gained much needed operator
experience for the potentially supporting user experiments in the
future, without being pushed out, thus providing the FEL with a deeper
pool of experienced operators.  We are beginning training sessions with
students on machine operations, allowing them to better understand their
important role in the success of the FEL.  The viewer walk code (known
as walking the dog) for automatically recording sets of beam viewer
images with a summary of the running conditions is being readied for
prime time.  The functionality for comparing them will begin after its
completion.  We are also training our student Matthew Stokes on the
basics of Tcl/Tk programming.  He will be working on the design and
implementation of an automated mini-phase procedure for his student
project.

The Alignment Mode System was re-certified earlier this week.  This took
a good portion of Tuesday to get completed due to minor tweaks in the
system. These were necessary to ensure a safe and useful system.  Once
certifications were completed Rich and Dan took advantage of the
unallocated machine time to continue with Multi-pass BPM studies.  They
spent the first portion Wednesday doing the initial setup and recalling
all of the software configurations required for the timing cards.  Once
setup was completed we tried to get Multi-pass operations while using
the existing electronics.  After examining several possible problems we
took some power measurements on the machine during CW operations at 500
uA, the power that we found coming out of the BPM was on the order of
-37 dBm.  This lower power appears to be our problem with making the
Multi-pass BPM system work out of the box.  In an effort to continue and
get some functional design that can separate the two beams we looked
into using the RF-DC Converters to replace the electronics and produce a
signal that can be viewed on an oscilloscope.  For the RF-converter
board, we are concerned that we have been using a certain family of
power supplies that have been too noisy for this application, but if so,
we can easily correct this if it is the case. At the end of our studies
of IPM1F04A, we decided to move forward with a better integrated test
set-up that will minimize the time required to set-up and break-down as
our opportunities to work on IPM1F04A occur. As a final solution to the
multi-pass BPM (working at frequencies above 1MHz), we are investigating
an approach that uses high speed samplers with built in peak-detection
processing. This appears to be the most promising approach to the
problem. As a result of discussing this problem at the PAC05 conference,
we have made arrangements with an applications expert from Acqiris
([www.acqiris.com](http://www.acqiris.com/)) to come today and show us a
very promising high-speed DSP product that might be an out-of-the-box
solution.

A timing circuit for delaying the switching of the 100 Amp H-Bridge
switch for the sextupole power supply is in progress.  A prototype is
being built up for testing.  The specifications required for this switch
and all of the necessary components is being compiled so that all
parties involved will have a firm background of what the final system
goal is.

In preparations for the upcoming Nanotube experiments, the Nanotube
Table Motor Control Interface chassis and remote control box were
removed from Lab 1 for upgrades.  Modifications were made to the remote
control box to allow for remote operation of the Nanotube Collector, Air
Bypass Valve, and a +5/-5V motors.  Additionally, fabrication of a
second remote control box is in progress to allow local control as well
as remote control of the Nanotube apparatus.  A patch panel for video
feeds was installed and Twelve coax cables were pulled into Lab 1 for
the nanotube experiment.  All twelve can be found in EPICS on pull down
menu 4 of the FEL Video Control Screen.

Final pieces of the Lab 3 Terahertz Hutch also came together this week. 
This week the door and mat interlocks for the LPSS were installed and
tested.  The AC power was also installed in the hutch by the
electricians.  The transport line penetration was filled with expandable
foam to prevent gasses from tunnel to leak into the hutch. A camera was
installed in the hutch for safety purposes for monitoring activity in
the hutch and the lab camera is being moved to monitor the entrance into
the hutch as well as other activity in the lab.  The flat-screen local
monitor video cable was installed so it can be accessed through EPICS. 
The activities in Lab 4 will also be completed by the end of the work
day today barring any problems. The cables are in place for the
flat-screen monitors and the camera for monitoring the lab is being
installed.

Three more Temperature Diode Crates are being assembled.  The backplanes
have been completed, wiring for all the power supplies is nearing
completion, and AC connections have been completed.  The rev'd drawings
for F0273 have come back from Dave Williams and were reviewed.  Planning
for incorporation of the RTD circuit into the board is being looked
into.  Mechanical fabrication of the 4 Channel Solenoid Failsafe
Interlock test box panels is complete and wiring is in progress.  On a
side note, the back room desks were cleaned this week, for more working
space for the 5 of us.

**WBS 9 (Transport):**

***Sextupole (SF)***

•   Fabrication continues at New England Techni-Coil. Forty of the 66
coils are wound. Completion of the primary machining/ grinding on all
core parts is scheduled for next week. Coil mounting pieces and field
clamps are almost complete.

***Replacement Chicane Dipoles GW)***

•   Fabrication is continuing at New England Techni-Coil. The first
dipole assembly, gluing of the Purcell gap pieces of the second core and
completion of winding the fifth (of 8) coil are all scheduled for next
week. Machining of the top and bottom pole plates of the third and forth
dipole started.

***UV Line***

• Magnet Test tested the standard QX Quadrupole using both the Danfysik
and the Power Section (Suitcase Prototype) of Trim Card II. They were
not able to detect any difference in the results using the three-stage
linear ramp protocol with "setting" from the polarity direction of the
final setting. The resolution is still at the 2 parts in 1000 realm.

• They tested two additional QXs to get some statistics, including #17
that was taken out of the FEL for suspect fields. Number 17 is a good
quad, but one of the batch that had smaller core dimensions. (We suspect
its problem was the centering offset number was wrong and will generate
a new one.) Results of the tests are good, but the limited resolution of
the probe system limits any finer analysis.

• Magnet test is still considering introducing a hall probe into the
quads at a fixed spot that could measure the actual field at a constant
point during all tests and cycles to establish true repeatability. To
investigate this concept and to get to know what is happening with the
QXs in the IR FEL, we will perform a similar test in situ on a known
sensitive quadrupole during a down day next Tuesday with the Bang-Bang
ramp, under various setting and hysteresis conditions.

• One of the two remaining regions being designed by the Engineering
Group is in check and the second is well on its way to full design.

• The sixth (GW Chicane) sub-region, chamber and stands, drawn by
Advanced Energy Systems is in signature.

### UV Wiggler Progress 

• No progress on the new Wiggler vacuum chamber.

***IR PM Wiggler Vacuum Chamber Progress***

• No progress on the new Wiggler's vacuum chamber.

**WBS 11 (Optics):**

***FEL mirrors:***

The two HR cavity optics that we tried our new procedure on came out
beautifully, with less than 1/10 wave aberration across the entire
diameter (2\" for the 1 micron HR, 3\" forthe spare 2.8 micron HR).  We
haven\'t had the opportunity to warp them, but will next week.  The 3\"
1.6 micron OC\'s have cleared metrology, passing all specs.  We hope to
measure the absorption with our vacuum calorimeter next week.  These
mirrors are the first set that were specifically engineered to reduce
the harmonic loading on the HR.  The reflectivity at the second harmonic
is of order 0.5%, while at the third harmonic, it is slightly over 20%. 
This reduces the amount of harmonic loading on the HR by 10-15 W over a
conventional quarter wave stack.  One OC was bonded, using the latest
iteration of our low temperature braze technique.  This resulted in a
slight compressive stress that warped the mirror to a slightly shorter
ROC (but still within tolerance).  There is about 0.5 wave of
astigmatism over the entire diameter, resulting in 0.05 m of ROC
change.  This is within Steve Benson\'s spec, but since we have some
time to redo the braze, our plan for now is to try again.  Discussions
with the vendor of the 1.6 micron mirrors led to our decision to drop
the requirement for a metal undercoating for this coating run.  By
adding a layer pair, they can lower the throughput of the fundamental
from 100ppm to \~ 5 ppm, and they will carefully ensure that the
reflectivity at the third harmonic is a maximum.  We should have these
mirrors by next week, and have them ready for installation during the
down period.  This is also true for the 96% R at 1.06 micron OC mirrors.

*** Other activities:\
***   Work this week began with the failure of a lamp in the drive
laser.  The replacement was fairly rapid, but there was a loss in cavity
alignment, so we struggled a bit (\~ 4 hours) to get good performance
again.  We\'ll look carefully at the alignment during the Tuesday down. 
The new style mechanical shutter has worked quite well all week, it has
more handling capability than the older version, so we believe it will
be more robust.  It is mechanically much better damped.  Operations went
fairly smoothly, the new HR is a dream, it warps beautifully, and as
detailed in the Operations section, is our first chance to try out some
of the theories proposed by W. Colson and coworkers at the Naval
Postgraduate School.  However, due to the high cavity magnification, we
see \"water wiggle\" on the outcoupler that is a hassle to deal with. 
During the down we will work on some passive ways to reduce it, and get
ready to try the OCMMS feedback circuit to reduce it further.  This is
contrary to the NPS prediction, but it probably reflects the fact that
right now we don\'t have the peak current required to be where the
theory is applicable.  With some more optimization we should be.  We
sent a few hundred watts of 2.8 micron into User Lab 1 and did some
studies on the affect of the mode with the new collimator mirror.  It
seems we need a bit more power on the DMA to get the correct ROC, but it
does work nicely.  Transmission to the OCR (90%) is what was expected. 
At this writing we have a mysterious loss in reflectivity (after only
two bounces between the OCR power meter and the power meter in User Lab
1.  We think it was due to a misalignment of the power meter and will
check that later today.  Good progress was made on alignment of the
optical transport that routes synchrotron light from the first arc to a
port upstairs.  This will allow more bunchlength characterization with
the streak camera to be done.  Part of the group attended the
FEL Workshop at the beginning of the week.  I presented a report on the
advanced drive laser.  We had some useful discussions, I in particular
held some planning and strategy meeting with A. Ogloza at NAWC China
Lake.  Shukui Zhang attended part of the CLEO conference in Baltimore. 
In an oral talk, A. Dergachev from QPeak gave a talk on the advanced
drive laser they built for us.

***UV FEL\
***We received multizone temperature controllers for heaters that will
be used in our bakeout jackets.   I failed to mention last week that our
first use of the cryopump for the HR optical cavity assembly was a great
success.  We are contemplating a similar system for the UV assemblies. 
We continue to iterate on a plan for cryocooling the optics.  Our first
measurements indicated that a flow rate of 5 gms/sec of He is a bit more
daunting than thought.  This was done in the Mirror Test Stand, with the
relatively floppy Newport gimbal mount.  More measurements will be done
once we get some mounting adapters for our prototype gimbal mount
fabricated.  We received the second strongback.  We also received most
of the parts for the diagnostic viewer assembly, that will be installed
near the HR.  The \"double-sided viewer\" concept was checked and worked
fine.

**Terahertz:**

Work continued on installation in lab 3, and also on the paperwork
approval process to ensure that we operate safely, treating the THz beam
as a class 4 laser.\
\
A meeting took place at Brookhaven to discuss THz instrumentation.
Present were Larry Carr, head of the THz program at BNL, Randy Smith,
BNL, Professor David Naylor, U. Alberta, and a PI on the THz program at
the James Clerk Maxwell telescope, the Herschel THz telescope and
several other programs, and Ken Wood from QMC instruments.\
\
David presented data taken using a new Mach-Zender interferometer using
newly developed metal-mesh beamsplitters.  The device is novel in that 2
beams are used, and one can be used to help reduce source fluctuations.
 The discussion also included ultrafast and other detectors and this
helps our current procurement process.  And still on the subject of
detectors, a preliminary safety meeting took place to prepare for an
engineering review of the cryogenic vessels in which the detectors are
mounted.