# MEMORANDUM 

**To:** Distribution

**From:** F. Dylla

**Subject:** FEL Upgrade Project Weekly Brief - June 13-17, 2005

**Date:** June 17, 2005

**Highlights:**

We devoted most of this week to tweaking the machine for high power
operation at

2.8 microns. By week's end we had optimized the lasing efficiency at low
currents:

lasing efficiencies exceeded 1.5 kW/mA at low pek charge (70 pC) and we
obtained 2.5 kW cw at 2.5 mA and 3.5 kW at 5 mA. Metrics of excellent
lasing were observed: long detuning curves (12 microns); short laser
turn-on times (8 microseconds). We obtained a good view of where we are
and we can come back to optimizing this configuration after our planned
two week shut down from June 20-July 5^th^.

During this shut-down we will be installing the high power 1.6 micron
optics, installing and replacing various beam viewer diagnostics and
vacuum isolation valves, and laying out a good portion of the UV FEL
chicane.

Also this week, we completed the laser certification of the experimental
hutch in the THz User Lab (3a) and obtained THz spectra with this new
configuration.

The first of the 750 MHz cavities for the 100 mA injector which were
manufactured by AES, completed processing and was tested at 2K. The
measured gradients (28 MV/m) exceeded specifications by a factor of two.
This result equals the best of the performance we saw with the entire
production run for 804 MHz cavities for the SNS project. These results
are timely for today's ONR/JTO project meeting held in Arlington for the
AES/JLab 100 mA DC injector project.

Tonight before we shut-down for the maintenance/installation period we
will be qualifying the transmission of high power 2.8 micron light into
User Lab 1 and delivering some test beam to the NASA/CWM nanotube
experiment.

**Management:**

The project monthly financial reports for May were completed and
forwarded to the Program Offices. Detailed planning of the staffing and
budget allocations for FY2006 continued.

On Wednesday, the detailed plan for next week's shut down was reviewed.\
\
This week had a number of interesting and productive meetings with
visitors.

On Monday and Tuesday of this week we hosted Peter Weightman, one of the
3 principal investigators on the 4GLS (FEL) project in the UK, and 3
colleagues. Their purpose of visit was to investigate opportunities for
scientific collaboration in the THz regime.  They have received new
funding to establish a THz beamline and facility and they presented a
preliminary design.  However, they expect several programmatic
interruptions due to scheduling of the first UK FEL (the ERLP), and the
upgraded machine. They would like to bridge those periods by
collaboration with JLab.

On Wednesday we hosted Prof. Dave Reitze from the Dept. of Physics at
the University of Florida. Dave is PI with the LIGO Project who is
involved with the high power optics and lasers which are the critical
components for these two large gravity wave observatories. We have been
keeping track of LIGO's progress in the development of low loss, high
power optics at 1 micron. Their current state-of-the-art is optics that
have absorption losses less than 1 ppm and scattering losses less than
20ppm.

On Thursday, we hosted about a dozen scientists and collaborators from
the US Army Night Vision Lab (Electronic Services Division).  At their
request we discussed the capabilities of the FEL and THz laboratories
and the visitors toured the facilities.  This meeting will help them to
formulate and co-ordinate future projects utilizing our unique light
sources. The Army NVL funds our THz program in collaboration with AES,
Inc.

Also on Thursday we hosted a visit by Prof. Avi Gover, from the Physical
Electronics Dept. at Tel-Aviv University, who also directs Tel-Aviv's
FEL Facility. Prof. Gover gave a seminar on recent results and studies
from his group.

We were informed that the FEL project proposed to the NSF from Florida
State received very favorable reviews in the first go-around.  The NSF
asked for clarification of some of the points raised by some of the
referees, and this week George Neil and Gwyn Williams participated in
helping to address these. FSU has asked JLab to be a partner in this
proposal.

**Operations:**

It was an interesting week.  Operations concentrated on getting a good
high power setup at

2.8 microns, 88 MeV.  We struggled this week to get both good matches to
the wiggler and good matches from the wiggler to the dump.  We
succeeded, perhaps a bit too well, in the first and only partially
succeeded in the second.\
The first part of the week was spent in careful setup of the 
accelerator.  Betatron matches were found, the dispersion
was suppressed, and the longitudinal match was optimized.  The laser 
lased reasonably well with this injected beam.\
We had not operated at high current yet with the latest injector setup
with stronger solenoid focusing operated 5 degrees off crest in cryounit
cavity 4.  When we did, we found that the pressure rose at the exit of
the cryounit proportional to the current.  Carlos Hernandez-Garcia
looked at this in PARMELA and found that, indeed, the beam was too large
coming off of the unit.  At this low an energy you need more focusing at
the exit of the unit.  The best way to get  this in our injector is to
use the first cryounit cavity (cavity 4)  focusing.  This does reduce
losses to reasonable levels but increases the bunch length going into
the linac.  This increases the  energy spread more than we would like. 
We were able to get a good match with this beam to the wiggler in both
the transverse and  longitudinal phase spaces.  The result was very
strong lasing.  The laser turned on to half power at the peak of the
gain curve in about  8 microseconds.  This is much faster than we have
seen to date and implies a gain of about 80%/pass.  The cavity length
detuning curve is also very long, also implying high gain.  The exhaust
energy spread, unfortunately was huge.  It is at least 12% full width. 
This is sufficiently large that energy recovery is nearly impossible.  
Half of Thursday was spent in a futile attempt to reduce losses 
sufficiently that we could operate at the peak of the detuning  curve. 
On Friday we tried to improve matters by reducing the charge.  The
interesting thing is that we were able to achieve 1.5 kW/mA efficiency
with only 70 pC of charge.  This corresponds to an efficiency of 1.7%. 
Since not all of the charge is participating, this implies that the part
that is lasing has about 2% efficiency.   One expects an energy spread
from 12% to 16% for this efficiency.   When an efficiency of about 1.5%
is exceeded the beam blows up near the dump in the last cryomodule and
trips off one of the last cavities.  This is due to uncorrected
chromatic aberrations for such a large energy spread.   With a little
tuning we were able to get 2.5 kW with 2.5 mA of beam and 3.5 kW with 5
mA of beam at low charge.   More careful optimization will be needed to
do much better than this.\
All this argues for several things:\
1 A cryomodule with a 3 inch aperture in the third position would
be nice (of course this is guaranteed in lower frequency structures.)

2\. Larger apertures in the injector would also be nice.

3\. A higher injection energy is required for this design.  We did look
briefly at operation with

8 MV from the injector instead of the 7 MV we have now.  We found that
we should be able to run there without too much field emission induced
vacuum rise.  We can look at this when we come back up.\
Other activities were conducted in parallel with the power push.  An 
effort was launched to align the streak camera to the light emitted 
from the first arc.  Some more work is needed on this.  User lab 3  was
certified for THz operation.  We can now do THz spectra and make 
modifications to the spectrometer as we wish.

We exhumed an old design model used back in \'01 to lay out the 4F and
5F energy recovery matching telescopes. This model fits beam envelopes
from wiggler to linac across the arc, through a range of momenta. Though
only crudely approximate to the installed machine (it lacks, for
example, the THz management chicane), it gave hints as to some of the
issues we are facing. First, the level of chromatic aberration in the
initial optics solution was pretty certainly seriously bad. Secondly,
the spots (with bright core and halo) we saw at 4F09, 4F12, 5F05, and so
on can be understood as showing the on-momentum betatron core and the
chromatically mismatched tails. Third, the wretched transmission down
the linac on Thursday was due in part to vast input momentum spread from
the insanely highly performing gonzo-journalistic FEL talking to a pair
of telescopes that had/have not been properly chromatically balanced.
Fourth, the improvements seen on Friday using a meatballed match
correspond to a better balance of the telescopes. Finally, and most
tantalizingly given the impending shutdown - there appears to be room
for additional improvement.

**WBS 4 (Injector):**

The DC photocathode gun is operational delivering beam for FEL ops with
a 43% request on the drive laser polarizer. A QE measurement was
performed this week by measuring the drive laser power needed to run 1
mA cw. The QE was about 4%.\
The aluminum cylinder for the NEG coating solenoid was submitted to the
machine shop for fabrication. The associated solenoid coil assembly
drawing was completed. Polishing on the segmented support tube
continued. More equipment from the FEL lab was moved to the ARC building
lab.\
The Si02N coated electrode was conditioned further and showed stable
operation at 25 MV/m, higher gradients generated higher emission at
acceptable levels.\
Work continued this week on benchmarking the 100 mA injector model with
AES results using  PARMELA LANL version.

**WBS 5 (SRF):**

This week we made a small but significant step by getting first hardware
in the ampere-class cryomodule project. It may not look like much but
from little acorns mighty oak trees grow, or so we hope. These are parts
for a copper model intended to validate the calculations of the
waveguide HOM dampers. We are doing this at 1500 MHz so we can test them
on a CEBAF single-cell cavity and get results quickly. The waveguide
dampers are key to obtaining BBU thresholds in the Ampere range while
keeping the cryomodule as short as possible. We are also making steady
progress on the 750 MHz cavity concept, tuner concept, cryomodule layout
and other ancillaries. The next step after the copper model test is to
make a niobium prototype.

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height="2.5909722222222222in"}

**WBS 8 (Instrumentation):**

The Terahertz lab was also completed (HONEST TO GOD!) this week. After
doing a little early morning searching in the lab and racks, the camera
for inside the hutch is in the system. There is also another camera
outside the lab that will be hooked up by the end of the day. The
hutch/room were then certified and commissioned to run terahertz beam
into the lab. The software for the power meter on the FTIR was also
installed on the new(er) dell inside the lab. After giving us some fuss,
the power program was cleanly installed on the PC and seems to be
working well.\
    Support for the video system update began this week with the running
of sixteen RG-59 cables from the video switcher rack to the control
room. The added features will be 32 instead of 16 outputs and up to 256
inputs. We are ready! All aspects of the new video system have been
fully tested and are ready to be installed at the start of the
maintenance down. We have 6 chassis on the bench which have been tested
and are ready to be installed. All of the CAN bus wiring has been tested
and each chassis has had its unique CAN system ID set. We have also
relabeled every cable in the system to include a unique database ID. In
the process, this act has functionally documented our existing channel
set-up and will allow us to quickly find \"the other end of that cable\"
and the full history of what it has been used for and what it has been
connected to as we proceed from here with our video system
configuration.\
    A final configuration and design for the 6kW polarity reversing
switch has been completed.  EECAD is currently working on the schematic
for the system PCB.  A prototype enclosure has been modified to
incorporate all the necessary connections and include the switching
electronics.  The power, control, and status will all come from the same
location so an external power source will not be needed.  A channel flow
chart is being completed to provide a graphical explanation of how the
system will function.  The backplane design has been completed for the
beamviewer crate upgrade.  The firmware programming first draft has been
completed for the beamviewer control card, this will provide the local
bus control for each card in the crate.  The design for the card is
still in progress with several details still being worked out.\
    Activities are also coming to a close in Lab 4. The security camera
is correctly in the system along with the area monitor inside the clean
room in the lab (after some serious snooping to find the power cables
for them). The two outside monitors are also in place and just awaiting
channels in the new video upgrade that will take place. Two of the LPSS
boxes were hung this week in lab 3A and lab 4 after the shipment of
unistrut and brackets arrived for them. The enclosure for the LPSS
Master that was sent to the machine shop also arrived and is ready to be
assembled.\
    Two of the revision C Cryo-Diode thermometer dedicated F0273 boards
came in assembled and were tested successfully. One of the two new
boards was installed in the already installed CTD chassis to fill it out
(16 total boards, 64 channels).\
    Extensive testing of the circuit boards for the GC power supply has
taken place. The boards were tested with the magnet setup both
individually and in pairs to determine the best combinations available. 
Screen shots of possible oscillations were taken, and from these the
source of the oscillations should be found.\
    Another beam viewer chassis has been repaired and checked out, and
is ready to support the UV upgrade.  The beam viewer test boxes have
also been repaired and are ready for use in aligning the new viewers.
Testing of the 4 Channel Solenoid Fail-safe Interlock PCB and box has
been completed.  The system is ready for installation during next
week\'s scheduled shutdown.  A 4 Channel Limit Switch Simulator box was
also designed, built, and tested in order to make testing of the system
less complicated.  A debugging procedure is being prepared for the
hardware. On a side note, to prepare for the upcoming shut down, we will
give a thorough check of all the completed CCD beam viewer cameras to
make 100% sure the ones that are tagged do and will work.\
    Moving in the new trailers continues; another shelf has been
installed over there, and all of the power supplies and transformers
have been relocated there.  Additional shelves have been assembled and
stored in the tent in continual preparation for the trailer move in.\
The needed correction to the lab safety application was made to allow
for the final certification of lab 3 (THz lab). The IOC reboot to
install the lab safety correction caused the polarizer to become lost,
creating a problem with the machine\'s charge per bunch. The polarizer
position was corrected with the help of Shukui Zhang.\
    We sent Richard Walker the miniphase procedure to help formalize it.
Working with David Douglas to record data on the ITV0F04 viewer to form
a reference point for after it is changed out during the upcoming down.
The automated miniphase (with the help of Matthew Stokes) is coming
along. The schematics for the required EPICS records have been drawn up
but not installed. Created an EPICS record that maintains a rolling
average of a given sample size (this will be used by the CEBAF software
staff in the future). We are working with Steve Benson for the design of
the goggle safety system. This will be an addition to the Laser
Personnel Safety System. Received HID Corp RF tag options for the
goggles. Looking into an Omron solution that will better mesh with our
LPSS\' PLC configuration.\
     Renascence cryomodule assembly continues; Terminated Piezo, Motor
Drives, Limit Switch wiring through the tuner ports on top of module. We
will install connectors once they are leak checked. Next week we will be
ready to install the 8 top hats, then we can terminate the Vessel
diodes, heaters, probes.\
    Coldfire 5282 mirocontroller was set as Autoboot, so that the
bootloader would pass control to the RTEMS OS image after 10 seconds.
The RTEMS will download database and records from an NFS server and
initialize the IOC. Database, device supports, and driver for beamviewer
control are under developing. Awaiting the beamviewer control card for
testing.\
     We are building up another \"mirror raster control board\" for the
\"photocathode response mapping system\" has been a major activity of
the week. We now have three of these boards built-up (including the one
installed) and we have documented the three jumper-wire modifications
required for the board to work. At the beginning of the down, when they
map the cathode, we plan to swap out the existing board and do an
in-system test of our new spares.

**WBS 9 (Beam Transport):**

***Sextupole (SF)***

• Work continues at New England Techni-Coil. Cores were assembled and
marked. Secondary taps to individual pieces is started. Pinning of cores
starts late next week. First coil potting had the inner mandrel stick to
the coil. They are working the issue. A vendor for ceramic tubes that
act to isolate the LCW circuit from the coil was found by Jlab's Larry
Munk and Tim Siggins.

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

• Work continues at New England Techni-Coil. The third core gets Purcell
gap glue-down starting Monday. The seventh coil (of 8) is almost wound.
Potting of the third coil starts next week. All core machining is
complete.

***UV Line***

• Set ability of the QX Quadrupoles of the UV Line was the object of our
investigations using the hall probe in one magnet this week. Magnet Test
found the Bang-Bang Hysteresis and Setting Protocol was just as good as
the Slow Ramp and has a good likelihood of repeating in the FEL
enclosure. Epics and trim card control of the field during tests can now
be done. Set ability of the actual field gradient integral is still
compromised by drift in the rotating coil stand at the level of ±2.5
parts in 1000. Ken Bagget is running tests using different data
gathering to attempt to reduce this band of uncertainty. In the mean
time, they believe they should be able to compare the strength of all
quadrupoles to the "Standard" Quad that was measured a SLAC using a
bucked measurement using the existing, long 2 inch probe.

• Girder assembly drawings and drawings for piece parts for Region
6Fsub1 were completed and are now in checking. Regional Assembly of the
8Fsub4 (Last) is in preparation

• Larry Munk is working at getting the existing inventory of surplus
girders converted to the required girders. We have seven that we can
start assembly with on July 6.

***UV Wiggler Progress***

• No progress on the new Wiggler vacuum chamber.

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

• The design of the wiggler chamber started.

**WBS 10 (Wiggler):**

STI Optronics has received the support structure for the IR wiggler.  
They expect the guide rails next Tuesday.  They tested the limit switch
repeatability and found that it far exceeded our  specification.  They
also looked at noise in the Heidenhain gauges and found none even when
all four motors were being driven.\
We had the kick-off review for the UV wiggler.  Since STI Optronics is
using most of the design from the IR wiggler for the UV wiggler, the
review was pretty simple.  A few minor action items were found.   The
design overall is very nice and should provide excellent service  for
the UV device.

**WBS 11 (Optics):**

***FEL mirrors:***

This week we completed the debonding of the 1.6 micron OC and rechecked
it\'s figure.  We now have a good optic.  The 1.6 micron HRs arrived,
and have a longer ROC than we\'d like.  We believe we found the problem
with the astigmatism in the 1 micron mirror; it is due to the silicon
dioxide coating on the back face of the optic.  While it is a rough
surface, we don\'t have good adherence.  We\'ve spoken to the coating
and glue vendors, and are regluing the optic after trying the quickest
of the recommendations, to soak the coated surface in acetone for 1
hour.  The

1.06 micron, 96% R OCs will ship next week.

***Other activities:\
***   We continue to juggle a number of activities this week.  We have
been moving all hardware not required for the next 6 months buildup
activities.  (A thanks to the gun group for ratcheting up their moving
activities to make more space for us.)  A drawing for a sizeable hutch
for the Dahlgren group was produced and sent to them for comment.  We
worked late last Friday to obtain more beam profile data in their
hutch.  (Thanks to Chris Behre for working late with them.)   We have
continued work on refurbishing mirror cassettes for Labs 2, 4 & 6.  We
ran high average power into User Lab 1 to look at the transmission.  We
have reasonable transmission into the OCR, but low transmission into the
lab.  We answered questions from staff from Daresbury about our
procedures. We also met with Prof. David Reitze, Univ. of Florida.  He
is associated with the LIGO optics core group measurements, and was very
helpful in providing corroborative information that verifies that the
loss of their optics (at 1064 nm) is about 1 ppm.  We welcome Jason
Taylor, a student from Old Dominion University, to the team for the
summer.  

***UV FEL\
*** We are working through the list of comments received from the
optical cavity review.

**Terahertz Project:**

The hutch in lab 3 was certified.  Visible synchrotron radiation was
observed on both diamond windows.  The TK Associates THz absolute power
meter interface card was installed and the meter was set up in lab 3.
Beam was restored to the Michelson and spectra were taken.