# MEMORANDUM 

**To:** Distribution

**From:** F. Dylla/grn

**Subject:** FEL Upgrade Project Weekly Brief - April 3-7, 2006

**Date:** April 7, 2006

**Highlights:**

Observations and results from this week's FEL operations:

> \- we obtained further data on the in-situ performance of both the 1.6
> micron and 2.8 micron high power mirror sets that installed in the
> outcoupler optical cavity
>
> \- the measured absorbed heat loss in the 1.6 micron optics has
> evolved from a barely measurable level at the beginning of the run
> (\~200ppm) in January to a value that is 3-4 times larger. Today we
> are installing a new 1.6 micron outcoupler optic so we can do
> head-to-head comparisons next week on this optical coating
> formulation. As a reminder when the absorbed losses are 200ppm or
> less, and the optics maintain their figure, the optical systems are
> not a limitation for 10 kW cw operation
>
> \- operation at 2.8 microns yesterday re-confirmed high lasing
> efficiencies in this optical set. We are planning to continue a power
> push at this wavelength next week.
>
> \- we continued to make progress on tuning up the RF power system and
> linac for high power operation. The system was stably operated at 5.4
> mA pulsed. This is always a more stringent test than cw operation but
> we used pulsed operation for set-up and observation of time dependent
> phenomena (such as mirror heating or RF transients).
>
> \- the NASA/CWM nanotube team had another successful carbon nanotube
> production run on Weds. evening running 75 minutes straight at a high
> production rate (\~5 g/hr)
>
> \- successful measurements of the complete spectral and temporal
> components of the FEL optical pulse were made this week using the
> "FROG" technique; this is a very useful diagnostic of the FEL
> performance

**Management:**

After meeting with representatives of the Engineering and SRF Depts.
last week, we distributed a priority list for FEL related tasks for the
second half of FY06. The scope of work on the list is consistent with
the available funding and labor resources. We attempted (in concert with
our colleagues in Eng., SRF, and PMO) to maintain key deliverables on
both the ampere class cryomodule design project and the joint project
with AES to assemble the 100mA injector cryounit. The original FY06
schedule on both projects had to be delayed because of the delay in
receipt of FY06 funds for these efforts.

We continued significant interactions with our eight partner
institutions in the drafting of our joint proposal to NIH due next week
for funding bioscience applications of the FEL. This effort is being led
by Eastern Virginia Medical School.

Next week (April 10^th^) we are expecting a visit for a tour and
briefing on the JLab FEL program by the Chief Scientist of the USAF Air
Combat Command, Dr. Janet Fender. The ACC is headquartered nearby at the
Langley Air Force Base in Hampton, VA.

**Operations:**

The original plan for this week was to try out the new optics, but they
were not ready in time for operations this week.  We therefore decided
to take some more data on the existing mirror set and to look more
carefully at beam quality degradation at high current.\
On Monday we recesiated and tuned up the injector.  The machine
came back well and we lased at about 2 kW.  This allowed us to check
out the new thermometry on the output coupler mirrors.  The newest
data showed much higher losses in the 1.6 micron output coupler than
when first run.  Tuesday\'s progress was slowed by phase drifts.  Some
more progress was made on checking out the injector. The beam had
shifted a bit before the cryounit.  This beam has been quite steady over
the last year so it has not been checked as often.  We also
installed better notch filters in zone 3 to reduce the occurrence of the
bad lasing mode.  This precipitated the need to tune up the RF
parameters on zone 3 again on Wednesday.  This was eventually a great
success.   We were able to run 5.4 mA pulsed beam for the first time in
over two years.  In 2004 we were running zone 3 at higher gradient and
the electron beam closer to trough and more nearly 180 degrees out of
phase with the accelerated beam.  This meant that the induced
phase shift when pulsing the beam was not very large.  The phase shift
induced under pulsed operation now is much stronger than it was then so
the RF system must be carefully tuned to keep the phase and  gradient of
the cavities under control.  Using this setup we were able to get up to
6.75 kW of power in 1 msec pulses at 2.8 microns on Friday.\
The 1.6 micron setup did not seem to lase as well as it had last
week and we're not sure whether this was due to changes in the electron
beam or the optics.  Dave Douglas noticed that the losses were increased
downstream of the wiggler and derived a new match to the wiggler that
reduced these losses by more than a factor of three.   The laser liked
this match better as well but it still did not lase well at 1.6
microns.  We therefore shifted to 2.8 microns and got an efficiency of
over 2%, about as high as that seen on March 24.  The efficiency for
pulsed operation at 1.6 microns is almost as high as before, too.  This
seems to agree with the mirror loss measurements, which implicate the
1.6 micron output coupler rather than the electron beam.

**WBS 4 (Injector):**

The cathode lifetime has been shortened due to a small leak in the
beamline between the gun and the quarter cryounit. We have leak checked
previously but the He partial pressure is too high to detect such a
small leak. We will leak check with Neon as soon as we can. Today we
re-cesiated the cathode taking advantage of the shutdown day even though
the percent request on the drive laser polarizer for full charge was
around 80%. The cathode delivered around 50 C of pulse and CW beam
during this week. We need to find and fix the leak to recover previous
performance when the cathode delivered more than 300 C between
re-cesiations. Today D. Bulllard is providing support to replace drive
laser RF cables. A new GaAs sample partially by ODU with alumina has
been mounted in the Source Group\'s cathode activation chamber in
preparation for testing next week.

Gun HVPS -- Observed 500 volt transients on the Gun output voltage
during the 5 ma pulsed mode operations.  This is larger than expected
and S. Benson is determining the necessary requirements.  During CW
operations even at high currents the ripple is less than 100 volts.

**WBS 6 (RF Systems)**

RF -- An additional set of RF heliax cables were pulled from the RF
Injector rack to the Divide by 40 chassis in the Drive Laser Clean
Room.  They were terminated and will be connected early next week. 
These cables are temperature stabilized heliax, installed with a water
hose (LCW) at 95 ± 1° F, inside a foam insulation tube that is inside a
PVC pipe.  The PVC pipe is tied to a cable tray to prevent movement. 
This task is to control any external sources of phase drift with the
Drive Laser.

 Additional oscilloscopes were added to allow Phase Measured (PMES) and
Gradient Measured (GMES) signals to be taken to the Analog Monitoring
System for viewing in the Control Room.  These signals were used to
adjust the various parameters of the RF Control Modules (RFCM) in Zone 3
to give good stable control when the machine is operated in pulsed mode
with high beam currents (5 ma).  The high frequency notch filters on the
Analog Boards of the Zone 3 RFCM's were changed to low pass filters with
a 200 kHz roll-off to better reduce any noise and ringing in pulsed mode
operations.  The screen software was changed to display Phase modulator
Bias (PBIS) with an increased resolution of 0.1 volts.  PBIS is one of
the parameters that is set to give good pulse response to the RFCM. 
Several of the Tuning Detector Offsets (TDOFF) for the cavities were
changed too much during the setup for high pulsed current and had to be
changed back for lower pulsed currents and CW operations.

 **WBS 8 (Instrumentation):**

Since the first part of this week was spent recovering from our
maintenance down, the injector was rephased using the script.  While
running the script it was found that a 40 Gauss magnet steer was needed,
this indicted that the beam was not centered through the cryo-unit. 
Once this was fixed the injector was rephased properly.  The next
important step for phasing scripts is our mini-phase set-up. 
The procedure is almost completed and is being reviewed so the
automation portion can be as much as possible.  The new user mirror
control screen was\
completed and tested.  The screen is now available for all to use.  The
third mouse button Duty Officer sign-in system is being updated with the
list of authorized personnel.  This provides a way for an automated log
entry to be generated so that accurate details of who is the Duty
Officer is on record.

    When Vernier Mode was originally requested back in Dec. 2005, Dave
Douglas also asked that it include a physical knob or dial that would
bring a \"vintage\" feel to using the system. Since the vernier mode has
been completely commissioned, we recently turned our attention to
secretly building Dave a tabletop \"knob\" for vernier mode. The result:
\"Ye Olde Knob\", which has been specially designed to go beyond
customary \"ten\" and provide the FEL operator with access to
\"eleven\". This week, we had the honor of presenting \"Ye olde Knob\"
to Dave (see figure 1). During the week we were able to use it as an
effective control tool for vernier mode. Please note that with this
special control tool, I personally believe we can achieve \"11\"
kilowatts.

**Figure 1: \"Ye Olde Knob\" for Vernier Mode control.**

![](media/image1.jpeg){width="3.248611111111111in"
height="3.9895833333333335in"}

Two new video switcher chassis were added to the system providing 64
more available video input channels. This brings the chassis count to 8
and a grand total of 256 active video channels. We are in the process of
designing a video switcher test chassis. More on that later.  We also
tested the video input signals for two different monitors in the control
room and noted the configuration as a way of reviewing our
installation.  The placements of the \"picture-in-picture\" positions
were established for the LPSS wall monitors.\
    Progress has been made in debugging the \"User Lab Status
Indicators\". We have chased some of the problems down to a connector
inside one of the IOCs. This ioc (iocfel7) is required to stray \'up\'
during that optics work going on in the vault. This is because the ioc
supports the LVDT sensors for the mirror positions. Therefore, fixing
this connector problem will have to be done when the optics folks say
they could tolerate losing the LVDT values.\
    An FEL OPs announcement (text-to-speech) system is currently under
test. It is essentially a zero-effort byproduct of the EPICS-to-Devlore
Project. In order to catalogue machine performance data from OPs (like -
what labs are made up and what the MPS trips are) we have developed a
system of machine event driven triggering of EPICS-to-Devlore data that
can easily be used to send a text string to a \"text-to-speech\" service
that runs on laser(.jlab.org). Extreme caution is being used in how this
service is introduced. For if it says the wrong thing - even just once -
I\'m sure it will be mercilessly smashed with a hammer.

    A method of remote programming our embedded IOCs has been configured
and tested.  We have figured out how to code a program to upload the
RTEMS Operating System image on to the ColdFire via the Ethernet. 
Basically a waveform record was installed on the ColdFire IOC, and on
the host machine.  We send a command to send the image file to this
waveform record, when the record is received, the image file gets burned
to the Operating System image on the flash ROM.  All of the updates are
done in the background without interrupting the Coldfire IOC normal
running state.  In order to load the new image the Coldfire IOC needs to
be rebooted and the flash ROM gets loaded onto the Coldfire.  Since the
method of remote programming required a reboot we added the ability to
remote reboot the processor from an EPICS screen.  With these two
functions, we have made a big progress on the EPICS-RTEMS-Coldfire
configuration.  This allows us to implement these embedded IOCs as we
would a VME IOC without losing any of the major functionality.

    The cooling plates for the Sextupole Reversing Switches were
received this week from the machine shop.  These are in the process of
having the water lines brazed into place and then the assembly of the
switches will begin.  Several more of the enclosures were gathered
together from the EES/DC group.  The metal work for the enclosures is
almost finished. The remaining few will have to be completed once the
first batch is done and traded with the EES/DC group so they can keep
their tests moving forward.

    Installation and checkout onto the beam line was completed for the
ND filter assemblies in the 3F region.  A fan out chassis was
fabricated and installed using one Beam Viewer channel in order to
control all the 3F filter enclosures.  Final preparation for ND2 filters
was made this week. Four filter assemblies need to be constructed and
these are the last remaining four.  Once the parts for these come in we
will be ready to go, to wrap up this project.  Two more ND filters were
glued and placed inside the filter boxes, these were installed on the
two SLMs at ARC1 and ARC2.  The PCBs that will be used for the ND-2
Filter Boxes in our Beam Viewer system were completed this week.  Fifty
of the boards were ordered.  These boards have implications in other
systems and test fixtures so some spares were ordered.

    Some time was taken this morning to investigate some the punch list
of problems that operations noted this week.  We looked into the 2F03
BPM to investigate why it wasn\'t responding to beam motion.  After a
couple of test it was found that a cable had broken or gotten damaged
over time in the machine enclosure.  The cable was replaced and that
took care of the response problem for the BPM.  We\'ve designed a
4-Channel Buffer Box that will drive an input at High Impedance and
loaded at 50 ohms.  These four channels have a gain of 1, 5, 10, & 100. 
We are currently in the process of constructing two of these boxes for
uses with the fast optical detector and other sensitive
instrumentation.  The panels have been machined and the wiring harness
completed.  The assembly of these will continue into next week.  Support
to the RF Group was given this week by install filtering on the existing
LLRF control modules in zone 3.  Also the test fixture for the SRF group
was finished for HOM Cable testing.  In the terahertz lab, a set of
shelves were put together for spare parts.  We cleaned up many of the
items from the back porch, these have been removed and taken to
storage.  The Happek insertable lens cover has been completed and
is ready for installation.  Time was spent with the Document Control
(DCG) folks to begin considering how their \"Oce\" system and our
\"Devlore\" system can be integrated to provide users with all of the
essential Oce capabilities embedded in the Devlore interface. This will
be fun.  A PC controlled Thermal Label Printer has been ordered. Plans
to integrate it into Devlore are in progress.  Preparation for the use
of lab 4 was also pushed along this week. Conduit has been installed for
most of the wiring for the LPSS system and final install/tidying needs
to be done so everything can be completed.  In lab 4, a set of cables
was run from the door to the LPSS box.  In association with that, one
plastic top piece for a cable holder was cut.

This week we have finished testing of the software, which controls our
Tektronix oscilloscopes connected to the Ethernet. The software also
gives us the possibility to download the data acquired by an
oscilloscope with 1 Hz rate. The data can be stored then and analyzed
offline. The software also can broadcast the measurements via Ethernet
for any other application so that the data evaluation can happens
on-line. For example we use this approach to measure on-line losses of
the optical cavity. Another example is making FFT of the data taken by a
scope, which can be applied to any signal. The software has been tested
and installed on one of computers in the control room and is available
to be installed on any other computer. The new software has been used
during this week to capture and store data for our experiment with the
LLRF as well as for some measurements with the FEL.

Since a temporal jitter of the electron bunches can be a very effective
way to reduce the FEL efficiency we would like to make measurements of
that jitter. This week we were looking for a best possibility to do the
measurements and learning how to make the measurements properly. We did
a good progress. The measurements can be done using the Beam Current
Monitor cavity (BCM) and the Agilent E5052A Signal Source Analyzer. We
think we are ready to do the measurement. We will need CW beam for the
measurements. The idea of the experiment is to measure the timing jitter
as a function of the average current and the bunch frequency. We did
some preliminary measurements when learning how to do the measurements.
We were measuring RMS jitter between 170 fs and 200 fs in the vicinity
of the wiggler in the range between 10 Hz and 1 MHz. The carrier
frequency is 1497 MHz. The figure below shows the measured spectrum of
the timing jitter. We have the possibility to make these measurements
right upstream of the wiggler as well as in the injector.

![](media/image2.png){width="6.0in" height="4.5in"}

**WBS 9 (Beam Transport):**

# *UV Line*

• We are working on developing a cost and schedule for starting the QX
Quadrupole qualification.

•  I finished the text of the draft of the UV Beam Transport Report,
added pictures and submitted it to Fred for review.   

# IR Machine Re-commissioning and Operations

•  I completed the building and installation of a step between the 1^st^
Arc's GY Dipole and the wall that will allow folks to safely go through
this narrowed zone and access the area of the 2G Dump.

• I will install the simple fiber optic array to direct a line of light
between the pole tips and the beam chamber of the Optical Chicane
Dipoles today.

• We continue working on using four uninstalled GW dipoles in a quick
experiment that uses laser light to look for a pseudoscalar particle
that couples to photons.  I designed the pole tip extenders for the GW
dipoles and am having one set made to prove the concept by a test in
Magnet Test.

•  I designed the cover for the W55 (IR Line) Wiggler and sent it out
for bid.

•  I worked on the design of the permanent cover for the optical
transport between the drive laser line and the entrance into the Light
Box in the injector.

**WBS 11 (Optics):**

#### FEL mirrors

This week we operated at both 1.6 and 2.8 microns and collected
calorimetry data (with the newly-installed thermometry discussed the
last two weeks), as well as gain and loss data.  At this time we are
still analyzing the data.  The new thermometry is quite responsive to
changes in the water temperature, responding in a few seconds, rather
than minutes.  Using the new thermometry, as well as information from
Ops, we are finding that the design of the scattered light shields was a
bit too liberal.  The shields are designed to not occlude the clear
aperture of the mirrors, except at the mounting points.  This allows
some scattered light to hit the mirror braze (or heat-conducting vacuum
paste) and holders, making determination of the loss in-situ
problematic.  To fix this, we are going to make some new adapters that
will completely shield the frames and mounts.  We hope to have those
ready for installation soon.

***Other Activities***

The anticipated receipt of the mirror frames we needed in order to
install new mirrors didn\'t occur over the weekend, so our plan B went
into effect and we were ready to lase again by the start of Ops on
Monday morning.  We received the frames yesterday, checked them, and
then used thermally-conductive high vacuum paste to mount a high power
(1.6 micron, 90% reflectivity).  This is the first time we have tried
using paste instead of braze for a mirror that will have a high
intracavity power load, and if it works well, would make the mounting of
mirrors for the IR Upgrade easier than it is now.  Conveniently enough,
as part of his senior project, Jason Tracy took data that will allow us
to extract the thermal resistance of the paste for future modeling.   We
operated the FEL last night to collect more data with our FROG (FEL
pulseshape) diagnostic, and this time used our spectrograph to record
representative spectra at the same points on the detuning curve.  Since
a spectrum can be calculated from the FROG data, the actual spectra will
be used as a benchmark to validate the analysis.  TMC #1 was checked for
residual contamination after a week long hot nitrogen purge, and found
to be clean.  It does have a leak, which we believe may be virtual.  For
now, we will store it for installation at a later date. With the release
of priorities, and funds, we are moving ahead with the completion of the
optical cavity mirror metrology system and some laser safety hardware
that will allow us to run beam to User Labs 2 & 4.  That and other tasks
will be updated in future weekly reports.

**Terahertz:**

This week, I was not able to take advantage of the evening beam
operations to continue power and imaging studies on the THz beamline
because I was reviewing the final design for the pump-probe vacuum
chamber and optics being built at Pike Technologies.  It was a
productive trip though, and all of the design issues were resolved,
allowing Pike to begin machining and assembly of the system.  It was
also a great opportunity to discuss the vacuum FTIR system built by
Pike, which is now installed in the hutch in Lab 3.  In consultation
with their engineers, it was determined that it will be possible to use
the signals from the vacuum FTIR to collect THz spectrum data when the
accelerator operates in pulsed mode.  Previously, it has only been
possible to make spectral measurements during CW operations.  This
expanded capability will provide much better diagnostics for the
accelerator operations when changing from pulsed to CW mode.