**MEMORANDUM**

**To:** Distribution

**From:** F. Dylla/grn

**Subject:** FEL Upgrade Project Weekly Brief - January 9-13, 2006

**Date:** January 13, 2006

**Highlights:**

As advertised in last week\'s report we brought the FEL Upgrade back
on-line on Monday after\
spending last week installing the UV wiggler and tweaking hardware in
both the FEL and electron beam transport systems.\
\
This week was spent  re-establishing agreement between the electron beam
transport models and the beam diagnostic measurements.  The gun cathode
had been subjected to a planned heat-cleaning the previous week and
recovered perfectly: we were soon able to run several milliamps CW and
lased at low power with the improved mirror figure.   We discovered a
few problems which were preventing our beam viewers and other
diagnostics from making calibrated beam measurements and spent a very
productive week working the careful details required before we can move
to very high average currents.   We are also working to automate our
injector script so that the beam performance is more consistent and
reproducible.\
 

**Management:**

We spent the week finalizing the FY\'05 Annual Report which should be
ready for production next week.  We also hosted Thomas Hodge of the Army
SMDC for a tour of the facility on Friday to give him a flavor of what
an FEL at WSMR might be like.

Invitations were sent out to key FEL users for enlisting their support
for organizing\
the up-coming FEL Users meeting on March 8-9. The preliminary
announcement for the\
user\'s meeting was distributed via our email database and posted on our
website.

**Operations:**

Operations started up again for the first time since the holiday break
and last week's UV wiggler installation.  Due to the fact that the CEBAF
machine is down this week we can only run day shifts and then need to
open up the vault.  Luckily, the initial turn-on was quite smooth.  We
were able to run CW beam to the 1G dump the first day and verify that
the BBU threshold was about the same as it had been when we shut down in
December.  The match was not very good but we were able to achieve
lasing at 1.6 microns on Tuesday with the relatively non-astigmatic
mirror set.  Due to the poor match, the performance was not very good. 
We also switched off the rotator and found that we could get up to 3 mA
of beam without BBU by using the trombone to suppress the BBU.  After
improving the match we were able to get much stronger lasing but the
electron beam setup was not very optimal.  We then spent the rest of the
week in more careful setup to get the injector, longitudinal match
and transverse match optimized for the laser.  We are now working on
a careful injector setup before optimizing the match to the rest of
the machine.

**WBS 4 (Injector):**

When the new photocathode was prepared last week via heat-cleaning, the
cathode scanner reported 4.5% QE while the drive laser power request for
full charge was the same as for previous cathodes with \~6% QE. We are
preparing to replace the green HeNe laser and check the electronic box
in the cathode scanner. The script for automatically phasing the
injector is being tested with actual beam in the machine. We are also
working in preparing a spare GaAs wafer and testing a different approach
to wet chemical anodization. We would like to have an anodized wafer
mounted on the spare cathode stalk ready to go in case we need it.

**WBS 8 (Instrumentation):**

A focus this week was the preparations required for the UV wiggler
instrumentation installation to begin on Monday.  The STI computer for
setting up the wiggler was delivered yesterday.  The wiggler\'s control
box was thoroughly cleaned and checked for any loose connections due to
shipment.  The strain relief for its signal and power cables were
installed.  Due to machine run time, the cables for the wiggler will be
dropped in over the weekend.

    The beam viewer alignment issues that were addressed last week are
resolved.  The alignment procedure is being updated after discovering
that the new viewer flags are much more sensitive to any linear
translations within the beam line.  The upgraded injector phasing script
is scheduled for testing today with planned beam time next week as well.

     In preparation for the newest magnet\'s operation, the
3F03 Octupole, the hardware has all been completed and connected.  The
cables connecting the magnet to the Trim rack have been installed,
labeled, terminated, and properly connected in the appropriate
location.  The 10 amp trim card that is needed to power this magnet has
been acquired and is ready to go in once the software for the magnet
control is ready.

    This week time was spent understanding and designing a Power over
Ethernet standard front end for a Powered Device.  The next version of
the Embedded BPMs will be PoE compliant (IEEE 802.3af) Powered Device. 
The necessary parts are being specified and will be ordered once funding
is available.  The circuit has been designed to be in accordance with
the IEEE standard has been laid out, this will be submitted for
documentation with the rest of the modifications to the Embedded BPMs. 
Also progress is being made in which direction to progress with sampling
the 4-Channels of the BPMs.  Currently we are under-sampling the signal
and therefore losing resolution.  Currently, the throughput of Embedded
BPM is about 100 Hz.  Our intent is to increase the sample rate so we
can average several samples that occur during the macropulse and then
provide a higher resolution position.   We think the throughput of
100 kHz will be necessary for the new BPMs.  The way we are going to go
about doing this is still undecided at this time.  The method of
implementing an FPGA to digitally average the signal is being looked at
along with the notion of averaging the analog signal before it is
digitized.  So, we are considering the use of an Altera FPGA to sample
the ADC and do the calculations. In the meantime, the FPGA
will communicate with Coldfire processor.  Development boards and
software for the FPGA has been installed so testing can begin.  We will
setup the system and design the circuit once we decide what exactly we
need to do.  Some time still needs to be spent exploring these ideas to
come up with the most efficient technique.

   The Proportional Valve Flow Status control box was completed this
week. The box is now completely assembled and just needs to be tested
with the actual hardware to make sure all is well. This will occur as
soon as the hardware is ready and time permits.  In preparation for the
Lab 4 LPSS box the mounting hardware is being gathered and modified as
needed before hand along with the cable raceways that get installed.

    The problematic fast valve that was in the optical transport line
has been repaired and tested.  Apparently one of the limit switches
inside the valve was not as it should have been and required
readjustment.  Supported gun work with a backup cathode and associated
systems and supplied technical vacuum support for the optics group.

An ongoing activity that has been making good progress behind the scenes
is the graduate work being done by Rich Evans under the thesis
advisement of Gwyn Williams. The field of study is the Far-IR
enhancement effects seen in the FEL due to the combination of high
charge in the micropulses and the ultra-short bunch lengths leading into
and through the FEL wiggler. In addition to making additional
progress in construction of a new rapid-scan vacuum FT-IR for Lab 3,
significant progress has been made on the theoretical side of the
thesis. Much of this week was spent learning how to generate stochastic
variables with arbitrary probability distributions and particle counts
greater than 10\^6. This was accomplished this week.  

The screenshot show below shows how this stage of the modeling works.

Below is a plot for the sinusoidal distribution for just 20k particles:

N = 20,000 and +/- 2 sigma (S=1) where:

#1 (Top-Left)

    \-- Continuous Probability Distribution:

    \-- F(x) = abs(Sin(2\*pi\*x)) \* e\^( (-1/2)\*(x\^2))

#2 (Top-Right)

    \-- 20k stochastic data points were generated per #1

#3 (Bottom-Left)

    \-- Relative Histogram of #2 into 200 divisions at 0.02x ea.

#4 (Bottom-Right)

> \--Re-normalized plot of histogram data showing histogram peaks as \"
> \* \" 

![](media/image1.png){width="4.7444444444444445in"
height="3.8506944444444446in"}

View \"fel_ctrls\" archive at:

<http://www.jlab.org/ccc/mail_archives/ACCELERATOR/fel_ctrls/CURRENT/>

**WBS 9 (Beam Transport):**

# *UV Line*

• Sextupoles (SF) and Replacement Chicane Dipoles (GW) will be measured
when funds are available.

• QX quadrupoles are ready to be assigned and mounted to girders except
for the three involved in the fork truck incident. All work is awaiting
funds.

• The wiggler vacuum chamber and the NEG Pump cartridge holder for the
second corner UV chamber are the only beam transport design efforts
remaining. The second corner UV chamber fabrication is on hold in
fabrication, awaiting the above design and fit-up of the NEG holder.

# *IR Machine Re-commissioning and Operations*

•    We installed the anti-halo Octupole into the first part of the
return leg and hooked up the trim card. The controls in EPICS will be
installed during the down day on Tuesday.

**WBS 10 (Wiggler):**

This week we worked on getting everything set up for the visit next week
of STI Optronics personnel for installation and checkout of the UV
wiggler.  A potential problem of black dust found in the control panel
was traced to the Kollmorgen servomotor drives rubbing against one
another during shipment.  None of the dust got into the  electronics so
we cleaned it up and put them back together.  

**WBS 11 (Optics):**

***FEL mirrors:\
***This week\'s operations were devoted to setting up the accelerator
for high current operation, so there were no opportunities to lase at
high average power.  A careful look at the figure of the 1.6 micron
deformable mirror assembly (worked on last week) shows improved
performance around the range of ROCs we need to operate.  Work on FEL
mirror improvement concentrated on doing metrology on the witness
samples that will be coated by two sources.  We received sixteen 2\"
figured Si substrates, after inspection, some will be used as spares,
others will be coated for testing in the FEL.

***Other Activities***

The prototype OBPM that had been cleaned for UHV use had reduced
contamination, but still had an unacceptable level of contamination with
some type of hydrocarbon.  We set up a hot nitrogen purge and at this
writing, had reduced the level of contamination (as measured by an RGA)
by 100X, to a partial pressure of 1E -9 Torr.  We\'ll hot N2 purge
through the long weekend to further lower the contamination level.  To
complete the end-of-line diagnostics, we\'ve given the I&C group some of
our IR cameras to modify with 12V and video output connections.  We
recorded IR images of one of the cryomodule RF windows (cavity 6, zone
4).  We see no evidence of additional RF heating when operating the
linac cw at 1.5 mA of beam current.  Work has begun anew on the THz
pump-probe optical and electronic setup.  Work on the cryocooling of one
of the outcoupler mirrors has begun in earnest.   

***UV FEL***

The cryocooling effort discussed earlier is directly applicable to the
UV FEL.

**Terahertz:**

This week we continued work on the modification to the chamber after the
first focus that will allow us to view the first diamond window at all
times.  In lab 3 we set up the power meter and camera, so that together
with the Michelson that is already operating, we are ready to
characterize beam.