# MEMORANDUM 

**To:** Distribution

**From:** F. Dylla/grn

**Subject:** FEL Upgrade Project Weekly Brief - January 8-12, 2007

**Date:** January 12, 2007

**Highlights:**

This past week has been devoted to optics changeout and our exercise of
turning the machine around following this intervention. Last week we
installed 900 nm optics and during the first part of this week we
successfully lased on this new optics set in preparation for next week's
run of the ONR funded LIPSS experiment (Axion search) by Yale and
Hampton Universities. Following the 900nm tests, we installed new high
reflector (HR) optics in the HR optical cavity and successfully brought
the machine back into a lasing state by late morning today.

We took advantage of the down time this week to identify and remove some
slightly magnetized material from the electron beam transport system. We
also recesiated and re-conditioning the photocathode gun today. This
cathode delivered a record 545 coulombs since the last recesiation. This
lifetime has improved more than an order of magnitude since our first
experience with this photocathode system at the beginning of the JLab
FEL program.

Next week on Jan. 17-18th we are presenting a review of our
accomplishments during FY06 to a review panel assembled by ONR and
NAVSEA PMS-405. The review is scheduled to begin at 0800 at Jefferson
Lab (in Conference Room F113 in our main administration Bldg).

**Management:**

Much of the attention of management and our FEL system owners this week
was devoted to preparing for next week's annual review. We also
completed a detailed annual report and distributed this report to the
review panel and our Navy program managers.

On Thursday, Jan .11, we met with Capt. Kiel of PMS-405 to discuss the
contractual mechanisms for JLab FEL project funding during the second
half of this fiscal year.

**Operations:**

This week was dedicated to checking out the new output coupler
optics and installing one new high reflector mirror.  We turned on
Monday and tested out the new 900 nm output coupler.  We had not
installed the high reflector yet so we lased both with the broadband
high  reflector and with the 2.8 micron high reflector operated on the 
third harmonic of the coating.  We obtained lasing with both
high reflectors.  The broadband reflector deformer was not working so
the Rayleigh range was very long.  With the 2.8 micron high reflector
we could adjust the Rayleigh range to be optimal.  The gain was high,
the spots looked very round, and the mode was quite stable.  We ran CW
with both HRs.  The broadband HR only allowed for about 40 W in the
OCR.  This was due to the HR heating up and making a long Rayleigh range
even longer.  We obtained about 300 W with the 2.8 micron HR.  It also
had problems with heating since the third harmonic is very strongly
absorbed in the coating.  This will not be the case with the 900 nm HR.\
Tuesday we checked out the other output couplers.  The 1.6 micron 11% OC
worked as well as previous 11% OCs.  The efficiency was about 1.7% in
pulsed mode and the laser turned on in about 12 usec.  We saw strong
third harmonic lasing near the peak of the detuning curve and could
obtain lasing with 1.17 MHz beam.  We got up to 1400 W with 1.25 mW of
beam but did not spend much time optimizing the laser.  We lased pulsed
and CW with the 1.06 um cavity.  The OC for this cavity has a damage
spot in its center.  The mode likes to avoid this spot when running CW. 
We could get stable CW operation if we mis-steered the electron beam so
that the laser lased in a TEM01 mode.  This has a null on axis so it
doesn\'t see the damage spot.  The pointing stability is much improved
after lead straps were put on the OC.  We could not detect any movement
at the end of line for a couple  different collimation settings.  The
2.8 micron cavity lased quite easily at 0.93 microns.  We checked the
radius of curvature calibration and found it to be quite different from
previous measurements.  This turned out to be due to a change in the
cooling water temperature.  The gain looked similar to previous
measurements.\
Wednesday and Thursday we were down installing the new 900 nm HR as well
as new shields and gold-coated clips on the HRs.  We also recesiated the
cathode.  Today we are conditioning the cathode.  We have found that
running CW beam for a while right after the cathode is recesiated leads
to a very long lifetime.  We will start optimizing the accelerator for
900 nm operations on Tuesday.

**WBS 4 (Injector):**

On Thursday we recesiated the GaAs wafer for the first time since it was
activated into a photocathode in November 1, 2006. This photocathode
delivered a record 545 Coulombs and 60 hours of CW beam time without a
recesiation with the photocathode gun operating at a variety of currents
from 1 to 7.5 mA DC.\
\
We hosted the visit of Dr. Lee Jones from the ERLP project in Daresbury,
UK. Dr. Jones had a very productive visit discussing photocathode gun
technical aspects with the CEBAF Source group and with the FEL injector
group. He also gave an excellent ERLP update talk as part of the CASA
Beam Physics Seminar series.\
\
We continued with our experiments on finding the GaAs wafer heat clean
threshold temperature for surface roughening due to Arsenic loss. We
found that our usual heat clean temperature of 550C (as measured on the
wafer) is too high and roughens the GaAs wafer surface. The threshold
seems to be between 480 and 500 C. The appearance of HeNe scatter light
at this threshold is also supported by a slight rise in Arsenic reported
by the RGA. We will repeat the experiment in a more controlled way to
confirm the result.\
\
D. Bullard is providing support for attaching Cu cooling tubes on a
model of the wiggler chamber.

Gun HVPS - Fully operational on both drive stacks.  The HVPS tank for
the Gun Test Stand is in the room and scheduled to be installed early
next month.

**WBS 6 (RF):**

RF - Miram curve scripts were run this week for the Linac and the
klystron filament voltages were adjusted as necessary.  This will
prolong the life of the klystrons and ensure adequate cathode current to
generate the needed RF power.  The pick-off of the Drive Laser signal
for the Injector Phase Monitor was installed, but it was determined
there was insufficient power at this location.  It will be moved close
to the optical beam dump of the light box.

 

**WBS 8 (Instrumentation):**

A highlight for this week was the progress made on the Laser Personnel
Safety System (LPSS). Of the 7 user labs 3 have been updated with the
new local LPSS boxes, the other 4 have had their control cabling run to
the Optical Control Room and were wired into the master. Additionally
the new sweep boxes were completed and installed in the labs (see
student section below). More work was spent on the 4-Channel FEL BPM
Electronics this week.  The channel layout of the RF portion has been
completed and the specifications of the RF shields have been turned over
to the mechanical design student for documentation and design drawings. 
Some other work is being performed to see exactly what dimensions of the
enclosure we can get away with at a reasonable cost.  Once a decision is
made on this portion of the design the schematic and layout can be
completed.  Some time was also spent working on the Single Board IOC
PCB.  This design of the board will be implemented into the BPM
electronics in some shape or form and the verification of the
functionality is becoming increasingly more important.\
    The 4-Channel Beam Viewer Control Card was completely tested on the
bench successfully.  The PLD code was debugged and optimized to perform
the required functionality.  The drawings have been updated with the
required component values and are ready to go into document control once
they are signed off.  The backplane will be tested with control card
once the 3U General Purpose Processor card is ready to go.\
    Some work continued this week on the Sextupole Power Supply
Reversing Switch  installation.  All of the water lines were connected
to the manifolds and the entire system, including the switches were
pressure tested successfully.  There was also a meeting to schedule the
complete installation of the magnets, power supplies, and certification
procedure of the entire system.  A list of action items was created and
a follow up meeting has been scheduled for the 1st of February.  Plans
to install the remaining switches have been put on hold till a long term
plan is agreed upon.\
    The Power meter signal for the QE monitoring system was commissioned
so that we can read the signal into EPICS. Two failed VGA to video
converters were replaced; one for the OCR Tek-scope and one for the
control room Dell PC running the Spiricon software.  Also this week,
drawing numbers have been setup in the database for the \"new-new\"
embedded BPM circuit boards as well as numerous cable entries.
Programming problems cropped-up this week due to changes done last
weekend on the ELOG system. Specifically, the scripts that were written
to provide flog attachments had to be fixed to agree with the changes to
the ELOG database. Progress was also made this week in bring online the
generic operations accounts for both FEL operations and the JLab CUE
systems.\
    A new version of the Single Board IOC was completed. The
Coldfire-FPGA bridge code was loaded on the FPGA, and we found the
temperature of FPGA was unusually high. The current for the FPGA was
over 1A. When we check the board, we found that two bus transceiver
caused the heating. After the transceiver removed, the current and
temperature are normal. The Coldfire bridge in now functioning and can
communicate with the FPGA.\
    The UHV software was updated for the addition of the buncher ion
pump.  The reboots required for the update took place during down time. 
The readback was also added to the archiver.  The jumper cable needed to
route the buncher pump to the UHV power supply was made.  The
terminations on the HV cable for the pump were also re-terminated,
thanks Jim. Work was also done with members of the LIPSS group to handle
the data acquisition and data logging they will need.\
    From the students: This week was extremely productive.  Infused with
fresh determination this week we were able to install the sweep boxes in
Labs 1, 2, 3, 3a, 4, and 6.  We also ran the necessary cables to each of
the sweep boxes in order to hook them all together.  As a general test
we terminated the sweep boxes in Lab 1, applied 24 V to them, and
confirmed that the sweep boxes would work as intended. All that is left
for the sweep boxes now is to hook up the Sweep Boxes in Lab 1 to the
LPSS Box and to terminate all the sweep boxes in the remaining labs. 
Also this week we pulled two 20 conductor cables from the LPSS boxes in
Labs 3, 3A, and 6 to the LPSS box in the OCR.  On top of that we pulled
a 8 conductor cable from shutter box 1 in the vault to the OCR LPSS and
a 8 conductor cable from shutter box 2 in the vault to the OCR LPSS. 
Then in our spare time we finished installing the PPE boxes in labs 4,
5, and 6.  This means that there are now PPE boxes in all the labs with
the exception of 3A.

**WBS 9 (Beam Transport):**

***Improvements and Upgrades***

• With regard to SF sextupoles, we held a meeting to integrate the new
power supplies into the entire magnet system. The proposal is to test
the magnets with the power supplies in Magnet Test with the actual
software. Ramp rates for the hysteresis cycles became a large issue
because of the time they take.  Testing would resolve the path to get
the shortest times.

•  Concerning work on the second wiggler chamber, Eutectic 157 and its
flux does a good job of attach the copper tubing to the chamber.  We
used heat guns to get to the right temperatures without warping the test
chamber. 

• In work for the New Gun and injector Test Stand, McAllister Technical
Services continues fabricating the stalk retraction mechanism. The
fabrication continues for the aluminum shell that covers the apparatus
at the high voltage end of the ceramic stack for both the injector test
stand gun and the new upgrade to the gun in the vault.

•  With regard to removing magnetic anomalies from the beam line, we
changed out the remaining magnetic band clamp screw mechanisms on the
corrector dipoles. The replacement brackets for the GW Dipole Field
clamps will be available on January 15.  We replaced all the slightly
magnetic stainless steel bars and their screws and nuts that support the
chambers in both the arcs and the Optical Chicane.  The remaining item
is the studs that hold the field clamps in the GW dipoles of the Optical
Chicane.  Those parts will be ready on the 15th of January.

Experimental program

*Experiment to see a pseudoscalar particle that couples to photons*  

•  The LIPSS Group has all the optical mounts for the coated mirrors for
the optical path before the generator magnet.  The Brewster Windows were
mounted on the Generator Magnet vacuum system and both vacuum systems
for the Generator Magnet and the Regenerator Magnet are now pumped down
and on Ion Pumps (Thanks to the Vacuum Group).  A quarter wave window
for the Regenerator optical path was obtained from the folks at Old
Dominion. We are getting a loaner camera that more closely matches the
experiment's needs and it will be shipped today.  We mapped the magnetic
field in the doubled up dipoles.  The result was a substantially more
uniform field than we anticipated because of the overlap of fringe
field.  The January 22 start of the Physics run is realistic. 

**WBS 11 (Optics):**

**Cavity Work**

This week we focused our efforts on making changes to the High Reflector
(HR) end of the FEL optical cavity. We first qualified a new 900nm HR
Deformable Mirror Assembly (DMA). The astigmatism at 16.2 meters was
0.04 waves with a heater current of 350 ma in the Mirror Test Stand
(MTS). We replaced the metallic coated broad band mirror with this
optic. The current HR configuration is 900nm, 2.8um, 1.6um and 1.06um.
In addition to this mirror swap we added lead straps to all the pitch
rings except the for the 1.06um mirror. This position is too confined to
support a strap. These straps have significantly reduced the mirror
vibration of the mirror on the other end of the cavity. A strap was also
added to the Yaw plate and another to the front scatter shield. We took
this opportunity to replace all 12 SS fixed clip with the gold sputter
ones. The last change was to add a 2.5 inch aperture scatter shield to
the 900nm (3 inch diameter) optic. The 2.8um has a 2.75 inch aperture
for reference. This cavity work commenced on Wednesday and by Friday
morning all four cavity mirrors are aligned and ready for beam
operations.

 **Phase Monitor**

In an effort to supply a signal for the drive laser phase monitor we
attempted to install a fast photodiode near the injector light box. The
reflected signal from the near Brewster window was measured and found to
be lower than was is needed for a good S/N ratio. We will instead use a
pickoff from the \~50% reflection off the photocathode.

 

**Advanced Drive Laser (ADL)**

Further optimization on the LBO SHG generator gave over 26W power with
65% efficiency at 75MHz. For the 100mA injector, this laser will also
need to run at 750MHz with much lower pulse energy. This week we
investigated the possibility of maintaining the same efficiency with a
new harmonic generator. Our test showed high efficiency at low IR input
power but a significant SHG power drop and mode change occurred when the
IR power was over a few watts. We will analyze the data and check the
system for damage. The real-time spectrometer installed in OCR was used
with FEL light early this week and appeared very helpful for laser
operation.

**Terahertz:**

Work this week in the THz lab included preparing the vacuum systems for
the planned spectroscopy studies.  The repeatability tests on the vacuum
FTIR system in the THz lab continued this week, but are as of today,
still unresolved.  We have found that the signal to noise for the vacuum
FTIR system is roughly 10x higher than measurements made on the
unmodified FTIR bench in the ARC building.  We suspect this is due to a
misalignment of the source into the interferometer, but more tests are
necessary to verify this and more work will need to be done to check and
correct the alignment.\
\
The other work this week involved assembling and testing all of the
optics in the new sample chamber, as well as leak checking that chamber.
 A few leaks were found and we will clean those seals and leak check the
chamber again today.  The alignment and performance of the optics was
tested with an expanded HeNe laser beam and we verified that the beam
imaged perfectly through the system for a sample in both transmission
and reflection mode.

Megan Ivory, who worked in the lab during the holiday shutdown was a
great help in testing these systems while we made preparations for the
annual review.  She leaves today to start the final semester of her
senior year and will be missed by all of us.