# MEMORANDUM 

**To:** Distribution

**From:** F. Dylla

**Subject:** FEL Upgrade Project Weekly Brief - July 4-8, 2005

**Date:** July 8, 2005

**Highlights:**

This was a shortened week for most of us with the July 4th holiday.
However we accomplished our primary goal for the week yesterday
afternoon by returning the machine to lasing after the prior two week
shut-down for installation and maintenance activities. We lased at 2.8
microns using a new broad-band mirror high reflector that has the
deformable radius control that is a feature of our narrow-band, high
power mirrors. The lasing looked good-showing a long detuning curve
(\~15 microns).

This test allowed us to check-out all the accelerator and FEL systems,
including our first look at our newly functional \"multislit\" beam
emittance diagnostic in the front end of the machine.\
Several items fell off our list by the time we stopped the installation
activities last Saturday. Several beam viewer assemblies needed
replacement or adjustment and we did not have\
a satisfactory high power high reflector at 1.6 microns ready for
installation. The viewer assemblies are being taken care of today and a
1.6 micron high reflector that passes our QA test will be installed
tomorrow.\
\
Next week we begin the summer run with the primary goal of pushing the
power at both 1.6 and 1.0 microns.\
\
We had some important results in the SRF arena this week. The crew that
is preparing and testing the AES 750 MHz cavities for the 100 mA
injector has completed the processing and\
testing of these cavities. All four meet or exceed specifications.
Secondly, the SRF team had their first look at the HOM damping on a
single cell copper model with the proposed\
3-waveguide dampers. The HOM damping is excellent -Q\'s in 100-1000
range-which means BBU thresholds exceeding 1 ampere. Multicell tests are
next in line.

**Management:**

We had an operations planning meeting today to lay out the next two
weeks of operations. Dave and Steve will be leading the first shift
efforts for tuning the machine for high power operations at short
wavelengths.

We will use second shifts for back-up measurements, diagnostic
development and conditioning activities.\
\
Steve Benson has been invited to give an overview talk on the status of
high power FEL oscillators at this year\'s International FEL Conference
at Stanford (Aug.22-26). A draft\
abstract and list of topics has been circulated for comments.\
\
Per our loan agreement, we sent the documentation to Cornell University
on the gap motion mechanism that will be added to the Undulator A which
is on loan from Cornell for the UV FEL. Cornell responded with several
items that will be incorporated into the agreement and we are\
working to incorporate their requests.\
\
Gwyn Williams is attending a meeting of the scientific advisory
committee for the 4GLS project this weekend at Daresbury Lab.

Joe Gubeli returned from a week\'s visit with our partner, Aerospace
Corporation, to coordinate the visit by the Aerospace team to complete
the Laser Microengineering Station (LMES) in User Lab 4. This visit is
presently scheduled for the last week of July and first week of August.

***Beam Optics Ponderifications: (D.Douglas)\
***After hearing rumors of the BBU results for the next module, we kept
crawling (literally) back to \"rotator\". We have a rotator, sort of, in
the IR side of the machine, but don\'t - and don\'t really have space
for one - in the UV side. This is a freeing notion, as it means that no
readily available solution works, and thus we have to think of something
else that can be unconstrained by physical, project, and financial
reality.\
\
The \"something else\" comes out of the realization that a rotator is
just a bunch of skewed quads, and thus can be computed either the hard
way: using a large optics program that models skewed quads (hint:
WRONG), or by working out with pencil and paper, a very symmetric
arrangement of normal quads and then, and ONLY then, rotating it (hint:
RIGHT).\
\
If the latter approach is followed, one readily finds a means of making
a skew quad system that can be toggled between two states, one of with
is completely uncoupled, the other of which is fully coupled, and both
of which image the transverse match in exactly the same way. This
requires using 6 or more skew quads in 3 or more FODO periods tuned to
rational phase advances.\
\
Given such a system the rest of the machine can be readily tuned to give
a true rotation by simply imaging the (nominally round) beam from the
center of the \"bad boy\" module onto (a round beam at) the rotator, and
then inverse imaging back to the bad boy, but with the phase of one
plane shifted by a half wave relative to the other and relative to the
first half of the machine. In this case, the single turn transfer matrix
takes the following rather nice block form:\
\
\[ 0  I\]\
\[-I  0\]

***Related Beam Physics:***

K. Beard, E. Pozdeyev, and C. Tennant just submitted JLab TN-05-060,
\"Estimates of the Beam Breakup Thresholds in the 10kW FEL with the
Renaissance Cryomodule\" and showed 2 slides at

the Friday morning meeting July 8th.

The Renaissance cryomodule will be used to replace FEL03 to boost the
linac energy and gain further experience with the upgrade modules. Based
on the SRF groups\' best available measurements of the higher order
modes (HOMs) in just a few of the cavities, a number of Renaissance
style modules in the FEL were simulated. Three different codes were used
(two use the time, one the frequency domain); all were in agreement. The
results are similar to the results from a previous study, TN-03-035.

When using the IR line, the machine should see a beam breakup (BBU)
threshold between about 1.5-3 mA beam current, and when using the UV
line, between 2-3 mA. Both of these thresholds are well below the design
goal of 10 mA for the IR and 5 mA for the UV, so we will continue to
develop and exercise the BBU suppression techniques we demonstrated over
the last year to avoid this limitation.

**Operations:**

It was a rather short week, with a couple of down days and one vacation
day.  After a half-day of hot checkout, we got beam running Tuesday
afternoon and rapidly found a number of minor items that received
attention on a Wednesday maintenance down. When brought up on Thursday
(following a 3 hour morning down for dipole power supply repair), the
beam almost  immediately was recovered at the dump. We verified that the
QE was conserved - with 54% polarizer giving 135 pC  -  phased the
injector and linac very roughly, and noted that the  bunch length was
compressing reasonably well at the wiggler (both  from Happek and CSR
enhancement of momentum spread). There followed several short but
valuable tests:

> check out of Wednesday's I&C work - The new viewers looked very 
> good.  Other systems also seem to work OK
>
> multislit checkout - beam made it through both H & V slits (after 
> some gronking); we made estimates for re-alignment on Friday
>
> checkout of the GW shunt setting; we found it was of order 1%  off.
> This was verified as consistent with magnetic measurements by George
> Biallas and Tommy Hiatt: on the 80 MeV end of the 120 A  excitation
> loop, the GWs sag a bit. At the moment, we are shunting no current
> from the 4F chicane.

Following a steer-up, the system lased on the new deformable broadband
HR, producing (after some adjustment of the ROC and a bit  of tuning) a
16 micron detuning curve. Pulsed beam was recovered and energy
compressed, with minor effort alleviating some of the losses from
scraping. High power running was precluded as the vacuum into the
optical transport was not yet good enough to open up the appropriate
valve(s).  This also limited our diagnostic so that we  could not
determine the efficiency but only the cavity length  detuning curve. 
The latter is a measure of laser gain.  This is the longest curve we
have seen yet at 2.8 microns.\
\
Friday was another down day devoted to upgrading some diagnostics
and getting ready to install the high power 1.6 micron high reflector.

**WBS 4 (Injector):**

The gun came right up this week and continued to supply beam for machine
operations.

Design work and manufacturing of a tube mount for the W&M implant system
continued.

The second section of the segmented tube was cleaned and delivered to
the shop for welding of its base flange. Polishing of the third segment
of the support tube was started.

The second test electrode coated with SiO2N  by W&M was mounted into the
high voltage test stand and is pumping down over the weekend and will be
baked out next week This test will provide another data point to ensure
the thicker coatings viability.

Design drawings for the magnetron sputtering system continued to be
worked on.

**WBS 5 (SRF):**

100 mA injector update:

All four fundamental cavities have been qualified via VTA testing. There
does appear to be some losses due to the stainless steel end flanges.
Cavity (serial number) one will be retested with Nb end flanges in order
to investigate these losses.

JLab engineering has begun working on tooling designs for the various
assembly and processing activities associated with handling the cavities
all through the string assembly process.

Detail design work has begun on the warm-to-cold beam pipe assemblies
and is expected to be complete by the end of the month.

The third harmonic power supply has been shipped from AES to JLab. The
third harmonic cavity is gong through some additional testing at AES and
expected to be delivered once these activities have been completed.

The analysis of the HOM coupling requirements is continuing with a focus
on the power requirement for the feed through.

Ampere class cryomodule update:\
  We got a first look at the HOM damping of our three-waveguide design
on the single-cell copper test model, see pictures. Q\'s are very low,
in the 10^2^ to 10^3^ range as predicted by simulations. This bodes well
for the BBU threshold \> 1A for the multi-cell cavity. Next up we will
test this end group on an existing 5-cell CEBAF-shape copper model to
verify the multi-cell predictions.\
    We also busy preparing several posters on the JLab Ampere class
cryomodule work for next week\'s SRF workshop at Cornell.

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**WBS 8 (Instrumentation):**

The beginning of the week was devoted to the support of machine hot
check out.  The Machine Protection System for the vacuum interlocks was
certified as operational. The 0F03 multislit assembly and its associated
fail safe interlock was installed and tested successfully along with the
updated software and screens. The magnet transport system check out
revealed a failed control module for the Extraction string which was
repaired.  ITV0F04 was reinstalled and tested successfully following
modification of the shield and target assembly. Radiation damaged
cameras were replaced in ITV0F04, ITV1F01, ITV1F04, ITV1F04A, ITV2F03,
ITV2F06, ITV2F09, ITV3F04, SLM5F03, and ITV5F07.  The viewers were
focused and aligned following the change out and proper operation was
verified through several viewer walks.   The limit switches on ITV3F06
were repositioned to work correctly with the MPS.  The machine shop
delivered the new replacement parts for components in ITV3F12 and
alignment has begun on it. Although the old viewer is installed on the
beamline and its camera has been replaced, the new 3F12 will go in after
all of its kinks are worked out. The stepper motor assembly for the CSR
experiment in 4F06 needed a limit switch mount, so designs were drawn up
for it and 3 other motor assemblies.  Completed terminating signal
cables for the instrumentation diodes for the 1/4 cryomodule. A new
diodes crate will be installed at FL01B11 now that 16 new complete Diode
CTD boards have been programmed. The GC power supply chassis is
beginning to shape up.  The gain of several operational amplifiers was
changed to reduce oscillations on the output along with additional
filtering. Data was collected to determine the offset of the system, and
several spreadsheets were created for analysis.        

Time profiled the WesCam software to locate the time intensive areas.
Alterations to the program are being planned.  Corrected the problem
with the WesCam triggering at ITV0F04.  This will be tested with beam
Monday morning.  Calibrated the beam viewer cameras that have been
replaced.  A rewriting of the beam viewer camera manual has also begun.
Many of the unclear sections in the old version have been cleared up and
the instruction given in the manual is concise. The final sections are
coming together and will be ready by the end of the day today.

**WBS 9 (Beam Transport):**

***Sextupole (SF)***

• Work continues at New England Techni-Coil. Cores are being painted.
Full production of Coil potting is in process with 30 of the coils
potted. Brazing the coil adaptation fittings to the leads is started.

***Replacement Chicane Dipoles (GW)***

• Work continues at New England Techni-Coil. The glue down of the
Purcell gap on the fourth core had a hollow spot on one pole tip. NETC
stripped the sheets and is re-gluing. The fifth coil is potted.

# *UV Line*

• We continuing the path forward in qualifying the QX Quadrupoles of the
UV Line during the week.

> \- Unexplained uncertainty in our data from the trial bucked probe
> measurements at the parts in 1000 level has lead us to abandon this
> branch of our measurement strategy.
>
> \- We are concentrating on measurements of absolute strength to our
> required accuracy at an external vendor or Lab for all the magnets.
> The specification for that measurement is in its 4^th^ and final
> draft.

• Girder assembly drawings and drawings for piece parts for Region
6Fsub1 going to be signed on Monday. Regional Assembly of the 8Fsub4 is
nearing design completion.

• The existing inventory of surplus girders continues to be converted to
the required girders at a local vendor, due August 1.

• The Jlab Shop continued welding the upstream GW chamber and projects
completion of the chicane chambers by August 15.

• The Engineering group continued design of the downstream corner
chamber, filling out the details of the layout and simplifying the
construction.

# *UV Wiggler Progress*

• No progress on the new Wiggler vacuum chamber.

# *IR PM Wiggler Vacuum Chamber Progress*

• The design of the wiggler chamber continued. We are now addressing
issues of interface to the OCCMs and overall support.

**WBS 11 (Optics):**

***FEL mirrors:***

We worked a bit through the holiday weekend to ensure we would be ready
to run on Tuesday.  As noted in the Operations section, we had a nice
success with the deformable broadband HR.  At this writing we are doing
metrology while deforming our 1.6 micron mirror.  If it passes we\'ll
install it, if not, we\'ll debond it and redo it.

***Other activities:\
***Besides the work listed above, we returned to our tasks of readying
User Labs 2 & 4 to receive beam, and work on the improved OTS
components.  Specifically, the second section of the collimator was
brought over to the FEL building so we could begin work on it.  We also
began the mechanical assembly of turning mirror cassette \# 2 and the
prototype optical BPM (O-BPM).  More work was done in User Lab 2 to make
room for the new hutch (for the Dahlgren group).  We had a
teleconference with them to discuss placement of ventilation and other
modifications.  We also fixed a problem due to a slipped kinematic mount
in the OTS which prevented transport of beam upstairs.

***UV FEL\
***We are progressing with the procurement of optical cavity mechanical
hardware, specifically the optical cavity internals and the stands and
other hardware downstream of the OC vacuum vessel.  Drawings were
formally signed for the former, and signed for fabrication for the
latter.  The bakeout tents are in procurement.

**Terahertz:**

This week we continued with a series of experiments to understand the
absolute THz power meter.