**MEMORANDUM**

**To:** Distribution

**From:** F. Dylla

**Subject:** FEL Upgrade Project Weekly Brief --April 4-8, 2005

**Date:** April 8, 2005

**Highlights:**

This week we re-established operation of the FL03 cryomodule after
in-situ window surgery. The module appears to have recovered its
operation from before we shut down, delivering approximately 50 MeV.
With the total energy now available we should be able to run full power
at 1.6 microns and longer. Quotes have been received for high power
mirror coatings for this wavelength and we are preparing the order. We
will re-establish beam operation for lasing starting 0700 on Monday.

We hosted 150 attendees at the 6th International Symposium on Laser
Precision Microfabrication 2005 in Williamsburg, the first time this
conference has been held in the US. The JLab FEL got some great
publicity from P. Schaaf of Gottingen, Germany, showing the major
advantages of nitride coatings produced by the FEL over conventional
lasers. We also got to show off the new Laser Microengineering Station
for UV after assembly by Aerospace staff.

The IR wiggler gap mechanism passed final design review with only a very
few minor action items. We look forward to receipt of this system in
late summer.

**Management:**

We passed the 90% drawing review for the Injector Test Stand facility
modifications. We expect to be out for bid in 4 weeks.

We also approved the final design of two trailers to house staff across
from the FEL.

We established a tentative installation schedule for UV components on
the beamline. This will entail one week in late May, June, and July, and
two weeks in August.

**WBS 3 (Beam Physics):**

Activity Summary

The RF recovery period has provided an opportunity to ponder the design
of a compact driver for a high power FEL. We have a rough optics
solution for a machine with the following characteristics:

11 m long 748.5 MHz 6 (five cell) cavity module

30 x 3.3 cm period wiggler (99 cm); 0.4 m nominal betatron envelope at
center of wiggler

16 m optical cavity

These features were suggested to me by three people whose opinions I
very much respect, but who may not agree with one another, or, for that
matter, with any randomly (or deliberately) selected additional parties.
Any and all of dissenting opinion are invited to participate in a
celebrity cage match; I will gladly follow the instruction of the sole
survivor.

The resulting driver system is \~2 m x 20 m in footprint (Figure 1).

Sequentially, following the injection point, we allow

1/2 m utility slot

11 m module slot

1/2 m utility slot

1 m slot for extraction/recirculation

quad triplet

3 dipole mirror bend

quad triplet

4 dipole chicane around upstream end of optical cavity

quad triplet

wiggler

3 dipole THz management chicane (this can be skewed for BBU control if
needed)

2 dipole mirror bend

4 quad injection telescope (might be compressed to a triplet)

1.5 m slot for reinjection chicane

for a net of 12 dipoles and 12 quadrupoles (plus some assorted smallish
magnets

for injection, extraction, orbit correction, etc.).

The extraction/recirculation & reinjection chicanes may be compressible,
provided the adjacent quad triplets admit transverse displacement for
appropriate steering of the recirculated beam. This may save order 1.5 m
in length, though it will introduce some operational complexity that may
cloud the immediate value of the space savings.

A \"staircase\" injection line clone of the JAERI line (similar to the
CEBAF spreader/ recombiners) is under consideration; it will put the
748.5 MHz injector parallel and near to the linac axis just beyond the
energy recovery arc. This design attempts to incorporate information
from discussions at the ERL workshop; a reasonable but unoptimized
optics solution exists and awaits vetting by spacecharge simulation. The
need to manage THz radiation drives bending immediately after the
wiggler (as far as possible from the downstream optics); this in turn
encourages use of a fairly short return arc, clearing the energy
recovered beam well before the downstream end of the optical cavity,
even for

the relatively short 16 m cavity under consideration.

In consideration of the optical cavity length, we note that the
\"nearest\" pure (divides by 2) subharmonic lengths of 748.5 MHz (0.4 m)
are 25.6 m (64 RF periods) and 12.8 m (32 RF periods). Those considering
a 100 kW class FEL based on the shorter cavity length are invited to
follow guidance provided by

<http://mentalhealth.about.com/cs/psychopharmacology/a/antipsy.htm>

The longer cavity could in principle wrap completely the accelerator
footprint, but in practice would result in only modest parts reduction
(the upstream chicane would go away, but additional quads would likely
be necessary to handle the beam from wiggler to energy recovery arc; the
THz chicane is needed in any event) and, because of the length
contribution of that pesky injector hanging off the front end, might
actually make the overall footprint a bit longer than were it embedded
in the upstream end and hanging out on the injector side. Intermediate
subharmonic cavities (such as the selected 40^th^ subharmonic 16 m
cavity or a 50th subharmonic 20 m cavity) can be similarly
accommodated).

Reasonable optical solutions were developed for the injector (as noted),
both passes through the linac. A not unreasonable solution has been
developed for the energy recovery arc. A preliminary, unreliable,
inaccurate, and thoroughly state-of-the-prior-art model of this line
suggests, oh, a 10+% relative momentum acceptance. A rough and similarly
unreliably studied solution for the transport from linac to wiggler has
been developed; it needs work but shows some promise. I\'d include the
obligatory beam envelope plot, but the data are scattered across about
half a dozen different DIMAD runs and its lunchtime\...

![](media/image1.jpeg){width="5.997916666666667in"
height="1.1930555555555555in"}

Figure 1: Footprint of compact driver for 100 kW system.

**WBS 4 (Injector):**

We are designing a NEG coating apparatus large enough to coat the gun
chamber as well as the UV optical can. This facility will be installed
in our ARC lab being prepared now also with a clean area for gun
assembly.\
\
In an effort to understand the discrepancy on the cathode QE
measurements observed earlier between the cathode scanner and the drive
laser, we have done some calculations to see if the drive laser can be
used to measure the QE when the cathode bias is only 200V. The
calculations show that as long as the photocurrent stays below the space
charge limit for emission (500 nA at 75 MHz rep rate), we should be able
to make the measurement by attenuating the drive laser power down to
\~100 micro Watts on the cathode. We are planning to perform this
measurement early next week.\
\
On Thursday the photocathode gun was tested successfully to full
operating voltage (350 kV). The cathode QE is around 1%, which should be
sufficient for tune up beam operations.

**WBS 5 (SRF):**

-   Three of the four 750 MHz cavities gone through the first CMM QA
    check and two are proceeding through the chemistry and heat
    treatment processes. Flange seal parts are due in next week in order
    to support VTA testing activities.

-   A coordination meeting was held at AES & JLab this week in order to
    coordinate fabrication activities and the design plans for
    accommodating the inclusion of the third harmonic cavity.

-   The return end can assembly is complete. Final checkout is planned
    for next week. Fabrication of the supply end can was started this
    week with tooling setup.

-   Procurement progress, for cavity string components, remains on hold
    until AES receives their funding for this project.

**WBS 6 (RF):**

All systems were checked out for operation next week. Everything
successfully passed. We repaired some water hoses that were aging.

**WBS 8 (Instrumentation):**

The focus this week was to complete hot check out of the I&C systems to
support operations beginning Monday 4/11. We have been supporting the
re-commissioning of zone 3 for a good portion of the week. Aside from
these activities we are getting parts on order to support the source
team\'s effort to sputter NEG material in large chambers. This will be
used in both new gun chambers and optical cavities. Discussions continue
on how to get the required trim channels and what the field
reproducibility will be for the iron core quads. We have a few backup
options, stay tuned\...\
While working with Roger Flood from EECAD on the RF-DC Carrier Board and
the

4-Ch Filter Board it was decided that it would be more cost effective as
well as a better engineering solution to incorporate the 4-Ch Filter
Board into the single channel RF-DC Linear Converter PCBs.  This will
save the cost of two extra connectors, the Filter Board PCB, and provide
a better packaging design for structural support for each of the RF-DC
Converter PCBs.  The new RF-DC Linear converters with the filters will
be setup for 1.497 GHz RF signals with a 30 MHz bandwidth.  Plans for
remote attenuation variations is also being examined as this may be
useful for the various types of BPMs implemented throughout the FEL. 
Several evaluation boards have been ordered to examine the various
component parameters.  The first draft of the 4-Channel Carrier Board
has been completed by EECAD.  The carrier board completion is currently
limited by the design of the enclosure for the carrier board and the
RF-DC Converters, which is underway.\
Construction of the THz hutch in lab3 continues.  With the last week\'s
delivery, 90% of the skeleton of the hutch has been completed to date. 
The few remaining support beams were received from the machine shop
within the last day, and will be installed by Friday 04/08/05.  Side
panels have been trimmed and measured for mounting hole placement.
Installation of LPSS hardware on the lab 4 inner doorway is in progress.
Two pairs of Sentrol position sensors have been installed.  All
remaining parts for entry control and status for the doorway have been
ordered.\
\
          

IOCFELT2 in Lab 5 is now back up and running. This is our dedicated
AMS/Video test IOC. Getting all the pieces back to functional order
took-up most of the week, but we were successful and were able to fully
test-out our first 32 channel video chassis yesterday. Now that the
testing hardware and software have been put through their paces, we will
be able to test out the rest of the chassis quickly.\
We have met with Pavel, Carlos, and Nobuyuki to review to LabView
Multislit program that Pavel had developed for the ELBE radiation source
at FZ Rossendorf.  The IMAQ module used by LabView for the image
manipulation is not available for Linux (our frame grabber runs on Linux
NOT Win\...). N. Mather, an applications engineer at National
Instruments, stated that there are currently no plans for porting IMAQ
to Linux.  Other routes for the image manipulation are being
researched.  The epics2devlore system is being configured to run on the
OPS workstations as well as Linux for testing purposes. We are beginning
to convert from EPICS 3.13 to 3.14, first on development machines.\
Mike Dickey is putting together the drawing cross-reference data for the
UV line (Regions: 6F, 7F 8F & 2V), we are importing the \"full\"
document control drawing list into our controls database to incorporate
his drawing cross-reference data as a way to navigate the controls
database. The Document Control Group\'s (DCG) MS-Excel \"Mechanical
Drawings\" spreadsheet file has been imported and the methods of setting
up pointers is being pursued.\
There was a design review video conference with STI concerning the new
wiggler jaw assembly. On the controls side there were no significant
issues. The previous patch cable for the GPIB control cable for the
AMS - felscope2 oscilloscope has been replaced with the permanent
installation cable.  The 4-Ch Pre-Amp chassis was modified to handle the
Happek signals generated by the two different power supplies that are
currently used.  The chassis was tested and the modifications are being
reported to EECAD for documentation.  Preparations were made for the LPM
Consortium Tour that took place this past week as well as for the
upcoming JLAB Open House.

**WBS 9 (Beam Transport):**

***Sextupole (SF)***

• Fabrication is continuing at New England Techni-Coil. Core parts are
starting final machining. Coil winding form and mold are in manufacture.

***Replacement Chicane Dipoles GW)***

•   Fabrication is continuing at New England Techni-Coil. Steel core
pieces for the third and fourth set of two dipoles are done. The first
coil is being prepared for potting. The fourth of eight coils is wound.
They are starting work on the Purcell Gap piece glue down procedure.

***UV Line***

• We started testing a QX Quadrupole with a linear ramp hysteresis loop
in a number of runs to gain reproducibility data.

• Tim Whitlatch has an idea to insert NEG cartridges into the downstream
corner chamber, eliminating the bake requirement.

• The 3 of five sub-regions layouts of the UV branch (less the chicane)
received comments and are being prepared for signature. They continue
the designs of the four stand and girder types that we don't have.

• The next priority item to sign off is the stand placement points so
that the Survey and alignment folks can start laying out the stand
positions -- no progress.

• Advanced Energy Systems submitted the stand drawings of the stands GW
chicane for checking and they are authorized to start detailing the four
chambers.

• The Jlab Shop continues modifying the prototype SC Sextupole to the
new SS configuration that meets David Douglas' criteria. Tommy Hiatt is
poised to put it on the Test Stand the Week of April 11 to verify the
quality.

***UV Wiggler Progress***

• Argonne National Lab working up a preliminary cost for the Chamber and
have sent it to their business office to add the Overhead costs.

**WBS 10 (Wigglers):**

The Final Mechanical Design Review for the 5.5 cm period variable gap
wiggler as held this week.  The detailed design looks good.  A few minor
suggestions were made.  STI Optronics should be able to send out the
order for the strongback next week.  They have received the Heidenhain
gap gauges.  They tested the gauges and found an accuracy of 0.2 microns
over their entire range.  We determined that, with a new routing of the
cables, a 68 foot cable length would work.  Routing the cables through
existing cable trays requires an 80 foot length.  STI Optronics is
exploring whether 80 foot cables are possible to obtain.\
All documents for the source selection board for the Cornell wiggler
modification had been signed off.  All vendor questions have been
addressed so far.  We have established a design for the vacuum chamber
that the engineer at Argonne agrees they can build.  Argonne has
finished the initial pricing effort for the vacuum chamber.  The final
price estimate should be available next week.

**WBS 11 (Optics):**

***FEL mirrors:***

A procurement request for 1.6 micron high power coatings on our existing
substrates was released today for award.  This is the wavelength we
believe should have the best performance given the available machine
energy, wiggler parameters, and optics capability.\
\
Metrology continued on the cooled mirrors for the optical transport
system to prepare us for providing light for Navy and other users in the
near future in Lab 1.\
\
We performed a readiness checkout of the optical systems in preparation
for running on Monday.  All systems go.\
\
The group attended the Laser Precision Microfabrication Conference to
get up to speed on laser capabilities and techniques of other groups,
especially the strong industry efforts in Europe and Japan.  This has
strong relevance to our efforts in material studies and modification as
well as reliably controlling high power beams.

**Terahertz:**

Work continued in Lab 3 on construction of the hutch and safety
interlock systems.  Specifications were drafted for a vacuum chamber for
pump-probe experiments.