**MEMORANDUM**

**To:** Distribution

**From:** F. Dylla

**Subject:** FEL Upgrade Project Weekly Brief --April 18-22, 2005

**Date:** April 22, 2005

**Highlights:**

This week we first concentrated on low power lasing (only 300 W.
Remember when that was not so low?) at 2.8 microns with the linac at
88MeV for continuing our commissioning of the optical transport and
certification of the Laser Personnel Safety System (LPSS). We then
re-tuned the linac for operation at 115 MeV, so that our broad-band
operation at 1.7-2.8 microns could be established. We delivered over 100
W to User Lab 1 for the first time in 4 years and demonstrated
continuous wavelength tuning from 2.1 to 3.1 microns using our broadband
cavity.

We finally fixed some pesky problems with one of the large magnet power
supplies in Arc 1 (thanks to assistance from the EES team) and we rung
out some problems with alignment mode operation which is essential for
user operations.

Frequent discussions are being held with our user group from Dahlgren
and the Harvard user group for user experiments in May using the current
low power configuration. We are expecting the completed optics for high
power operation at 1.6 microns by the end of May

**Management:**

George Neil, Fred Dylla, and Michelle Shin attended this week's meeting
of the FEL Technical Working Group (TAWG), which provides guidance to
OSD's Joint Technology Office for laser development. The TAWG listed
three high priority areas for JTO investment: (1) high current, high
brightness injectors; (2) ampere-class cryomodules; and (3) associated
resonator/optics components for high average power generation and
transmission.

We met with our Mechanical Engineering Dept. to map out the priorities
for the second half of FY05 and to project preliminary labor needs for
FY06 to support the FEL program. Coordinates for layout of three of the
zones for the UV chicane in the FEL vault were released today.

**Beam Operations:**

Progress was slowed this week by problems with one of our dipole power
supplies (thanks to the EES group for troubleshooting this).  We also
spent quite a bit of time debugging the alignment mode chassis so that
we could commission this mode for User Lab 1 (see the instrumentation
section for details). Seven FEL group members passed the FEL operator
training that teaches FEL Operators how to operate LPSS for the lab. 
They are now qualified to deliver FEL light to users.  More operators
will be trained next week.

On Monday we worked on commissioning the optical transport system to
User Lab 1.  We measured the power at several points in the optical
transport and found large reductions in the power getting upstairs.  The
fraction of power getting upstairs was a strong function of the radius
of curvature in the collimator so part of the problem may be vignetting
in the transport line.  We were able to deliver over 100 W of 2.8 micron
light to User Lab 1.  We then attempted to certify the alignment mode
system and found that the signals were not available for the alignment
mode chassis.

On Tuesday we debugged the alignment mode chassis and fixed several
problems.  In the end, however we still had spurious trips of alignment
mode in the chassis.  We also lost most of the afternoon to problems
with the Arc 1 power supply.   In parallel with the alignment mode
chassis work, we switched to the broadband hole output coupler and tuned
the laser from 2.1 to 3.1 microns while looking at the macropulse energy
on a pyrometer.   This allowed us to see that the power was relatively
constant over most of thewavelength range until the shortest wavelengths
were obtained.

Most of Wednesday was lost to work on the Arc 1 power supply.  Several
problems with the supply were found and corrected.  By the end of the
day it was working nicely.  While work progressed on the supply we
worked on optimizing the gradients in zone 3 to produce the most
gradient with the least field emission from the zone.  We found a
reasonable setup that produces 41 MeV of acceleration.  It is not clear
whether we can run much higher than this without some helium or pulse
power processing since the field emission levels rise rapidly with
gradient.  We can operate stably at 115 MeV.

Thursday we  worked on optimizing the 115 MeV configuration.  By late
afternoon we had a configuration that would run 1 mA CW to the energy
recovery dump but had a rather long micropulse.  One expects the bunch
length to adiabatically damp as the energy is raised, so the bunch
length should be less than 300 fsec FHWM.  In fact the pulse length grew
to 500 fsec from 400 fsec, indicating a large increase in the
longitudinal emittance.  We were unable to obtain lasing with this setup
so we are studying this configuration to determine what is so different
from the 88 MeV configuration.  Understanding this difference may allow
us to better understand the mechanism of longitudinal emittance growth
in ERLs.  The thrust of the work today is to better understand the 115
MeV configuration and optimize it for FEL operation.  Good progress has
been made. Once lasing is obtained we will optimize the setup and see
what power we can deliver to User Lab 1.

**WBS 4 (Injector):**

Good progress was made this week in setting up the new lab in the ARC
building. The DI water system was installed and is operational. The
clean area for the gun assembly is almost complete. Some items for doing
magnetron sputtering (to NEG coat the gun chamber) have been ordered.

Progress continues with the machining of some gun components. The
chamber tube and end flanges have been roughed machined.

The DC Photocathode gun is operational. The quantum efficiency has
degraded only slightly since the cathode was recesiated last week.

Gun HVPS -- Operational with no known problems.

**WBS 5 (SRF):**

[100 mA 750 MHz FEL Injector Cryounit]{.underline}

-   CMM, visual inspections and frequency measurements have been
    completed for all four fundamental cavities. Flanges and sealing
    material is due to arrive next week.

-   A detailed activity schedule for the 100mA FEL injector module has
    been developed and is being integrated into the SRF Institute
    project management process.

-   Instrumentation requirements and specifications are being clarified
    for design and procurement between JLab and AES.

-   Project schedule continues to slip, due to no activity on
    procurement or engineering tasks associated with critical cavity
    string and cryomodule components, all related work remains on hold
    until AES receives their funding for this project.

[Ampere class cryomodule]{.underline}:

    We are making good progress on the cavity geometry, HOM damping
scheme and cryomodule layout for the next generation, Ampere class
cryomodule. A simplified damping scheme with three waveguides on each
end (vs. four previously), seems to work well and is easier to package
(fig. 1). We have developed a revised cryomodule layout for this
configuration with staggered end groups that allows straight upgrade
style Helium header and fill lines or an SNS style helium vessel (fig.
2). The new layout may also save up to a meter of beam-line length by
moving bellows to the warm end regions. We are looking at options for
the tuner and helium vessel and have calculated the spring constant of
the new larger cavities. They are stiffer than the SNS (beta\<1) shape
but well within the capability of conventional tuners.\
    We have also completed the RF design of a scaled waveguide window
based on the PEP-II 1 MW design and are ready to start engineering and
modeling and seeing how to package it in the cryomodule layout.

![](media/image1.jpeg){width="2.998611111111111in"
height="2.2618055555555556in"}

Figure 1 New end-group and helium vessel concepts (scaled CEBAF cavity
shape shown).

![](media/image2.jpeg){width="2.6277777777777778in" height="2.09375in"}

Figure 2 possible cross section for straight Helium return pipe using
staggered end groups.

**WBS 6. (RF)**

All RF zones are operational.  Zone 3 has been experiencing higher than
expected radiation levels that have changed over time.  This has caused
a gradient reduction in zone 3 and an increase in zone 4.  The
monitoring of PMES for the Drive Laser and Buncher continues.

**WBS 8 (Instrumentation):**

The markups for the next generation Beam Position Monitor (BPM)
electronics have been submitted to EECAD. These include the
mother/daughter RF-DC Converters and the 4-Channel Carrier Board  The
enclosure boxes have been ordered and are expected to arrive early next
week for machining.  Once the documentation is ready, enough printed
circuit boards will be ordered to make up 4-5 sets for testing and
prototyping.  The design for the machining of the enclosure boxes has
begun as well as preparations for incorporating an onboard processor for
communication. 

Ongoing alignment mode certification effort - We have been battling a
number of problems this week in trying to certify the alignment mode
permit system. The top-level symptom is that the alignment mode permit
chassis (the device which measures the FEL electron beam structure and
informs the Laser Personnel Safety System (LPSS) if the requirements for
alignment mode are acceptable) will not reliably provide the required
permit signals that the LPSS demands to enter into alignment mode. As a
result, we can not successfully complete the Alignment mode portion of
the LPSS certification. Having worked through the some initial problems,
namely, decreased signal strength from ICM0F06 (-70 dBm) and having to
reprogram the onboard logic (Altera PLDs), we are now left with one
problem to resolve. We have determined that the 1G dump current signal
coming upstairs has too much noise on it for the alignment mode permit
chassis to properly digitize a 100mV signal. The dump current scaling is
1mA=1V and so 100uA of beam is instrumented as a 100mV signal. 100uA is
critical because it is the lasing threshold of the FEL. These repairs
were made to the chassis and a filter box was installed on the incoming
1G03 Dump Signal to reduce the signal to noise ratio.  We are current
perusing a solution and we hope to have the dump current issue resolved
by COB today.

With the exception of Lab 1 and the OCR, all the LPSS boxes have been
modified with a 12 volt DIN rail power supply and relay to support the
new iCLASS HID card readers.  New card readers were installed in User
Labs 2, 3, 3A, 4 and 5.  Lab 2 LPSS will be operating the new card
reader along with the new LPSS database.  The system has been tested
successfully and torture testing begins early next week.

Fluorescent coating of the beam viewer targets with the newest grade
phosphor powder continues.  Five coats will have been applied by COB
today and the target should be turned over to the vacuum installation
group.  A design for a Flow Interlocked 2-Amp Heater box has been
completed.  Fabrication has begun on the local box and testing
will occur when the box is completed.

Troubleshooting optics instrumentation - We chased down a problem with
one of the optical systems temperature readback channels. It turns out
that one of the 64 channels of a VMIC 3122 (ADC-module) is bad. This
card has been added to our maintenance list to replace and as a
temporary work-around, we have moved the temperature measurement to
another channel.

We are in the process of updating the LPSS user database.  We are
awaiting the new serial port cards for the LPSS test machine.  Once they
arrive, User Lab 3A will be added to the test bed.  Sent in the CCPR
request to have lpss.jlab.org (the existing LPSS pc) taken off the
Windows automatic update listing.  This machine will be manually updated
bi-weekly at convenient times.  Efforts are centering around preparing
for a LPSS switch-over.

The THz hutch construction continued this week and activities reach us
even closer to get a final product in lab 3 ready for use. The south and
north walls are up and secure. Three panels have also been placed on the
roof and are ready to be bolted down to the frame.

The fabrication stage of the video system upgrade is complete.  Chassis
are staged or testing which should be completed next week. Preparations
for returning to user driven operations have begun.  Operator training
is being held, labs are being made ready and assorted equiment that may
be needed by users is being assembled in a common location. Two
additional spare Dump Current Buffer/Driver boxes have been assembled
and tested.

**WBS 9 (Beam Transport):**

.

# Sextupole (SF)

•     Fabrication is continuing at New England Techni-Coil. Both types
of core parts, Hexagonal and Tee shaped continuing in final machining.
Coil winding forms are made. The manufacturer will pot these in a vacuum
tank in an open mold. Fittings will be added after. Conductor looks
good.

***Replacement Chicane Dipoles GW)***

•     Fabrication is continuing at New England Techni-Coil. A vendor
visit confirms that the first passed all hipot tests. However, there are
some whitish spots at high-pressure zones that didn't wet through. NETC
is authorized to coat these with an additional clear coat. NETC will
redo the mold we gave them to reduce the high-pressure zone and make the
mold more robust. They are preparing the core for Purcell gap glue down.
The core gap was uniform at the .0003 inch level parallel to the beam
and .00005 level transverse to the beam. This is very good work. We left
the special core gap-measuring instrument that reads at the .00001 inch
level to measure the remaining cores. We agreed that they have slipped
their schedule by 2 weeks, mostly because of deficiencies and subsequent
rework of the coil mold.

# UV Line

• The test of the QX Quadrupole with both magnet test power supply and
the power end of the Trim Card II showed that there was no difference
between field maps or current overshoots between the supplies during
linear ramp. Tommy Hiatt anticipates having to test all the quads
because the ramps between Bang-Bang and Linear Ramp are so different.

• Three of five sub-region's assembly drawings are having their
alignment point information checked before signature and pre-release
ordering has started.

• Advanced Energy Systems has sent their step file of the Debunching
Chicane Assembly to Jlab for checking and are through with the stands
and are detailing the chambers.

• The prototype SC Sextupole was not tested as we wanted because the
special bolts to fasten the poles were not received and work-arounds
didn't work. We expect the bolts soon.

# UV Wiggler Progress

•     No progress on the new Wiggler vacuum chamber.

**WBS 10 (Wigglers):**

Work continues on the 5.5 cm variable gap wiggler.  It is still on
schedule for an August delivery.  A thin layer of rust was found on the
pole tips.  STI Optronics will remove this rust as a warranty repair and
reapply some anticorrosion oil to the surface.

Bids were received from vendors for the modifications to the Cornell
wiggler.  They are being evaluated to determine the award.  A cursory
inspection indicates the bids are competitive and fall within the
budgeted estimates.

**WBS 11 (Optics):**

FEL mirrors:

The requisition for 1.6 micron cavity optics (and low outcoupling 1
micron outcouplers) was awarded, and we shipped the optics.  Work also
continues on the mirror bonding procedures, with the goal of greatly
reducing astigmatism that has been occurring.

Other activities:

 We had a great turn out for the Open House, so on Monday we spent some
time moving hardware back into User Lab 1 for use.  We have a complete
internal mechanical assembly of turning mirror cassette 1.  We have some
tolerancing that is too close, so drawing revisions are being made. 
Work on the laser hutch around the MTS in User Lab 2 progresses.  We
have issues with vibration isolation between it and the MTS chamber. The
drive laser ran well, but the mechanical shutter isn\'t reliable at
all.  We are looking at other options.  We are preparing the big hutch
in User Lab 6 for the advanced drive laser and some other experiments,
such as the 1 micron mirror calorimetry and laser damage testing.  We
looked at our model for the OTS at 2.8 microns and found excellent
agreement with the spot size in the lab.  However, the spots are smaller
as you get closer to the optical cavity, contrary to the idea posited in
the Operations section (of beam vignetting).  Another hypothesis is that
we have some excess absorption from one or more mirrors, so RTDs will be
put on all the cooling water outputs, so we can monitor the absorption.

Michelle attended the FEL TAWG and Beam Control Meetings in DC.  During
the latter meeting, she conferred with attendees on the DMA astigmatism
issue, and traded information on 1 micron optics.

UV FEL

The design or the optical cavity internals continued to progress. 
Procurements were started on the diagnostic viewer assembly.  The first
strongback was received and spare rails were installed.  We are going to
assemble the prototype mount on it and test the overall rigidity. 
Vibration testing of the prototype mount began. With a 4\" mirror
installed, the first resonance is above 200 Hz.  This is far above the
building resonances.  The drift and jitter of a commercial gimbal mount
was recorded for comparison to the prototype mount.  A preliminary
review of the data shows the commercial unit to be worse than the
prototype.

**Terahertz:**

Work continued on the installation of hutch panels, and on refining the
specifications for the chamber for pump-probe experiments. Discussions
were held with David Naylor of U. Alberta at Lethbridge regarding
spectrometers for the THz region. David has been involved with many
recent astronomical THz spectroscopic and imaging applications and
instrumentation developments. A meeting was held at Jefferson Lab with
Dieter Moeller (NJIT), Oren Sternberg and Ken Stewart (NRL) concerning
THz filters and interferometers.