MEMORANDUM

**To:** Distribution

**From:** F. Dylla

**Subject:** FEL Upgrade Project Weekly Brief --May 3-7, 2004

**Date:** May 7, 2004

**Highlights:**

This week we were occupied with the installation of the 3^rd^ FEL
cryomodule in the FEL linac and with the Navy review of the FEL
commissioning progress. The cryomodule installation went very well.
Final preparations were made last Saturday as soon as we stopped beam
operations on Friday. By Tuesday the module was in position, rough
aligned and cool-down to 4k was initiated. On Wednesday morning the
module was successfully cooled to the operational temperature of 2k. On
Thursday the RF waveguides were hooked up and today we completed the
vacuum connections for the upstream and downstream linac beam-line.
Sometime next week a final alignment check will be done and all the rf
and interlock connections will be checked out as part of the
pre-operations check. We thank all the staff that made the installation
of this important addition to the FEL Upgrade proceed so smoothly. We
required essential and coordinated support from the Accelerator Division
installation, alignment, vacuum, SRF, RF, cryo groups to make this
happen.

As noted in last week's report, we discovered a crack in GaAs
photocathode. In spite of the ability of the cathode to still provide
useable beam, we decided it was best to replace the cathode prior to
re-commencing operations. So we prepared for this change-out along with
some related maintenance and upgrades to the beam-line between the gun
and the injector cryounit. We have been running the machine every week
but one since the middle of November, so we have accumulated a number of
fixes. For the beam-line, a new ion pump, getter pump and getter--coated
beam-line were prepared to increase the differential pumping. Prior to
opening up the gun next week for the cathode change-out we prepared two
new cathodes from a GaAs material that has shown higher quantum
efficiencies (thanks to testing by the CEBAF Source Group), and anodized
a concentric ring on the outer circumference of this material to help
cut down on halo production. (We noted in the review this week that
subtle improvements made by Steve Benson on the drive laser transport to
the cathode had dropped our halo beam production from the 10^-4^ to the
10^-5^ level. We are hopeful that this masking procedure on the cathode
will also have incremental benefit on the halo production. Halo can
cause undesired gas desorption from and activation of beamline
components). Also during this maintenance period we are upgrading the
sextupoles so that these correction magnets can operate at the new linac
energy (\~150 MeV) provided by the addition of the 3^rd^ cryomodule.

In addition to our Navy program managers, we were fortunate to have most
of the members of our peer review panel at Thursday's review of our
commissioning progress. We found the opportunity of preparing for the
review useful for a self assessment of our progress-and as always- we
get useful feedback from our panel. In general the panel agreed with our
assessment that we had accumulated a reasonable understanding of the
current 2-cryomdule (88 MeV) configuration, and the time was right for
exploring the parameter space with the 3^rd^ cryomdule which completes
the original hardware specification of the Upgrade. We share concerns
with the current carrying capability of the new module because of
possible low damped, higher order modes (HOMs). Several useful
suggestions were made to help us plan our beam commissioning with the
new module. We thank Todd Smith for a useful suggestion on the use of
quad focusing to counteract the deflection of one possible deflection
mode if encountered. (You will note that Dave Douglas has already tested
our ability to use this option with his lattice model-see below). Also
Todd had a useful suggestion for helping us minimize the potential
damage due to gas burst induced arcs in the photogun by routing a signal
from our injector rf window arc detector to the gun HV control. Kevin
Jordan's I&C team started to implement this change in our machine
protection system today. (See below). A third action item from the
review concerns sharing of our FEL modeling parameters with Henry Freund
so that code comparisons can be made. Steve Benson's predictions of our
performance with the current 2 cryomodule and new 3-cryomdule
configuration using his spreadsheet and pulse propagation codes were
discussed at the review and related results are quoted below.

I thank the entire team and our panel members for all their efforts
which contributed to a useful review this week.

We congratulate our colleagues at Rossendorf who demonstrated first
lasing with FEL system today.

**Commissioning Summary (Steve Benson and Dave Douglas):**

Pulse propagation simulations were run this week to check out expected
performance with the latest electron beam measurements with both the
third cryomodule operated at 5 mA and the new permanent magnet wiggler
operated at 85 MeV and 10 mA.  Simulations were also done for 5.75
micron operation at 88 MeV and compared with measured lasing results. 
All the pulse propagation results were compared to the spreadsheet
results to benchmark the spreadsheet some more.  Good agreement was seen
for the predicted efficiency for the spreadsheet, pulse propagation
code, and experiment.  The spreadsheet and pulse propagation code agreed
with each other on gain but were a bit higher than the measured gain. 
The turn on time and detuning curve lengths agreed well with
experiment.  Performance at 2.8 microns indicates that, with the current
electron beam setup, we can get about 9 kW at 85 MeV with the present
bunch length.  If we shortened the bunch this goes up to over 10 kW in
the spreadsheet.  Pulse propagation simulations of the shorter bunch
will be done soon.  The three cryomodules run at 5 mA produces
approximately 10 kW for 5 mA for both the spreadsheet and the pulse
propagation code.  Both predict about 9.5 kW.  The gain is about 50% for
the new wiggler and 30% for the optical klystron and three cryomodules.

During preparation for the review, we did some reduction of difference
orbit data taken during the final day of running. A couple sample first
pass orbits (data and modeled) are attached. We found that consistent
agreement amongst the data could be achieved in the usual fashion - by
adjusting the transport quad gradient integrals by \~100 g rms - once
again confirming the excitation resolution lies at the 1% level.
Assuming a reasonably good match to the wiggler, forward- and back-
propagation of beam envelopes suggests the machine was not particularly
well matched towards the end of the run (Figure 2); this could
contribute to some of the largish emittances observed and reported on at
the review.

Given the restricted apertures imposed by the installation of Zone 3, we
are working toward more robust second pass orbit control. The data taken
at the end of the run include both first and second pass configuration;
we are trying to deconvolve the second pass positions from the measured
first pass behavior. As is evident from the orbit figures, we have
implemented HV coupling in the model.

Figure 1: Samples of 1st pass difference orbit data. Notice H/V coupling
on second pass through linac.

![](media/image1.png){width="6.491666666666666in"
height="2.671527777777778in"}

Figure 2: Beam envelopes. Some mismatch is apparent from the asymmetry
of the envelopes in the recirculator arcs, the ringing in the backleg,
and the large envelopes in the linac back end.

![](media/image2.png){width="6.49375in" height="1.3340277777777778in"}

As discussed in the Review, the following is the basic outline of our
commissioning plans when we come back up after this down time is
completed. We are working out the details and will have a complete plan
by close of business next Tuesday.

1.  Turn on FL03 at modest excitation and correspondingly turn down FL02
    and FL04, so accelerated e-beam is close to the configuration
    (energy) when we last ran with 2 cryomodules, & see how well the 3
    cryomodule configuration works under near identical conditions.

2.  Spool up beam power (current), in pulsed mode, and search for BBU.

3.  If not observed at, say, 5 mA, raise energy, retune, and iterate.

4.  If observed, start working though BBU suppression methods. (See L.
    Merminga\'s presentation at Review).

> At either of steps 2 or 3, recovery of lasing can be added as
> appropriate.
>
> Details of this plan will be fleshed out by C.O.B. Tuesday.

**Management:**

The focus of the week was preparing for and executing this week's Navy
review. We thank Gil Graff and the NAVSEA staff for taking the time
during a very busy time of the year for attending the review.

In addition to the review, we had folks traveling to and fro to cover
several other venues.

F. Dylla gave an invited talk on the JLab FELs on Sunday at the Division
of Physics of Beams session for the spring APS meeting in Denver. On
Tuesday, G. Neil presented progress reports on our JTO funded projects
at the JTO Project Office in Albuquerque. On Thursday and Friday, Gwyn
Williams and George Neil tag teamed our representation at a meeting at
the National Magnet Lab in Tallahassee concerning their plans to
incorporate a next generation light source.

**WBS 4 (Injector):**

Preparations are under way for the installation of the new wafer and for
adding more pumping to the beamline between the gun and the cryounit.

Gun: The stalk we had already cleaned and ready to accept the new wafer
had the wrong wall thickness tube, so it was cut and re-welded
yesterday. Today it will be cleaned with solvents and later heat-cleaned
under vacuum before mounting the new wafer. A new wafer has been
anodized and is ready to be mounted once the stalk is clean.

Beamline: The BPM to be installed will be leak checked today. The ion
pump and the NEG pump are ready for installation. A beampipe to be
installed between the buncher and the cryounit is in the process of
being NEG coated.

**WBS 6 (RF):**

Zone 1 - Work is progressing on the Gun\'s HVPS.  The HVPS tank is being
opened to clean the stacks and remove the Gun Resistor mechanism in
preparing for high voltage testing and zero adjustment.  The Quarter
cryomodule is to be cryo-cycled next week to remove any helium or
hydrogen gases.

 

Zone 2 - The cryomodule in this zone is also to be cryo-cycled next week
for the same reason.

 

Zone 3 - The cryomodule is in place with all operational cables
connected.  Additional test cables will be connected as needed.  It is
planned to test this zone on swing shift next week.

 

Zone 4 - This zone is fully operational.

**WBS 8 (Instrumentation):**

We are responding to another crazy idea that makes quite good sense;
during this week's review there was a short discussion of the beating
the gun has been taking to which Todd Smith responded \"Why don\'t you
turn off the gun (close shutter) prior to an arc in the RF.\" Looking at
things closer there was a delay added to the quarter arc detector trip
circuit to prevent false trips. This delay is \>100 microseconds which
is about the right time to potentially cause the problems we have.
Detailed measurements are underway and a direct connection from the arc
detectors to the Machine Protection System (MPS) shutter is being
implemented. BTW this is very easy to do because of the \"hooks\"
available in the system. The MPS firmware was upgraded to incorporate
the additional RF zone (3rd cryomodule). The RF FSD (P1) module was
checked out successfully and the permissive signal hooked up. Screen
changes were upgraded and the mask set for the FSD card was downloaded
and checked.

   All magnet leads and wiring along with ITV1F04 were removed from the
beam line prior to installation of the new cryomodule. Re-installation
of the 1F region power and signal leads is in progress. ITV0F02, the
cathode camera, correctors and solenoid power/signal leads were removed
from the Injector region in preparation for the gun bake. FELTECH1 was
replaced by FEL-SALLY in Lab 5, FEL-SALLY and FELTECH15 were upgraded.
Progress was made on the Convectron card test fixture and fabrication of
the SCL FSD/ MPS test fixture is complete and wiring is in progress.

  Final preparations are being made to the optical holder, cryomodule
electronic cover, and camera table. All finished products should be
returned to the FEL the week of 5/10/04. Continued support of the THz
beam line installation in Lab 3 and the 4F region. Additional stepper
motor cables were installed, terminated, and tested for the High
Reflector I & C rack to support the THz experiments. In order to
accommodate future requirements for the third cryomodule a Baratron
Power Supply was fabricated and installed.  This will provide
operational power and read back from the five Baratron Pressure
Transducers as well as provide an interface for remote EPICS read
backs.   The pre-fabricated jumpers were installed on the test sextupole
with the new \"add on\" coils for the Poles. All the magnet shunt
modules have been either upgraded or checked for correct scaling and
re-installed. The high voltage shunt for 4F00 was also installed. This
module has had their transzorbs removed and replaced with 450V FET\'s
with the read back scaled for 0-300 V. New 10 ohm water cooled load
resistors were installed for the Optical Chicane region. A test plan is
the works from D. Douglas to run the magnet strings with the new
excitation curves early next week.\
   The stepper motor controls for the drive laser\'s variable attenuator
began crashing repeatedly shortly after the installation of a new VME
board into iocfel10 for the drive laser\'s automatic switch to internal
RF (by auto switching with loss of master oscillator).After a few days
of careful inspection and troubleshooting, the problem was found. The
VME crate (iocfel10) for the drive laser controls requires that a jumper
be placed on the backplane if a card is inserted that does not handle
interrupts.\
   Progress is being made to enumerate and organize all of the
process/applications running on each of the iocs in the FEL as well as
all of the embedded controllers running in the field. As many of our
systems requirements have evolved over the years, we have grown overly
dependant on the \'expert\' knowledge of those few who are familiar with
the systems as they have been installed. For obvious reasons, the
software running the FEL and its related documentation is being included
into FEL configuration control. As part of the completion of the
Framegrabber manual, a system is being designed to simplify the process
of calibrating beam viewers and SLM\'s. Along with the intent of making
this procedure easier, it is being established to help eliminate
potential errors by the person performing the calibration. A user
friendly interface is being implemented that will present different
interfaces depending on the type of viewer being calibrated. The
instructions will also be specific to the viewer type. Backups will be
saved in order to provide a rollback in the event of an untimely miss
calibration. A log will also be kept to keep track of the changes have
been made and what the changes were.\
   Revision A to the Video Crosspoint Switcher board is on order and
parts are being purchased to complete the video upgrade.  The new
backplane boards for the Si Diode Thermometer Crate have been received
and are in the testing phase.  Parts are on order to complete this
project once the modifications to the circuit board are completed. 
Front and rear panels to complete the 4 Channel PreAmp Chassis are on
order and expected early next week.\
We have purchased two industrial oscillating fans for use in the vault
during maintenance.\
   The equipment in the conference room will be moved and covered today.
If there is other computer equipment in the areas that will be affected,
please let me know as soon as possible.

**WBS 9 (Beam Transport):**

***Sextupole Lite Re-coiling to obtain higher field***

• We split the magnets of the first arc, added coils and wired one up
for up for measurement in Magnet Test. Next week we will add coils to
the remainder of the magnets.

***Wiggler***

Electromagnetic Wiggler for 2.8µ

• Sixteen of 48 cooling plate halves have their brazing complete and are
being coated with clear coat.

• A first batch of 6 Kapton insulation layers is cut and being test fit
on the completed cores.

• Core machining is complete and it will be covered in clear coat.

• PECo is making two installation fixtures of bent lexan to handle the
conductors and insulation. The entire outline of the fingered fixture is
being made by water jet cutting.

• We shipped the second batch of Jlab supplied ancillary fabricated
parts and hardware for arrival at PECo on next Tuesday.

• We plan to visit PECo for start of assembly next Wednesday.

• We reached agreement on the additional costs of the wiggler associated
with details of assembly that were not available in the documents when
the contract was signed. These include mounting trim coils and manifolds
and combining the two units into one wiggler for shipping.

***Sextupole (SF)***

• Procurement on hold, pending 10 kW efforts

**WBS 10 (Wiggler):**

STI is assembling the poles onto the backing beams this week in
preparation for magnet installation next week.  The magnet measurement
setup is ready to go.  Final magnetic measurements are on schedule for
June 15.

**WBS 11 (Optics):**

**Plan A is to obtain low loss 6 um optics.  **

Additional metrology was done to confirm the new HR mirrors met figure,
ROC, and roughness specs.  A small flaw has appeared in both optics
since they were received last week.  So we can continue our progress,
one is being prepared for installation, the other will be sent back for
rework. 

 

**Our three Plan B\'s had the following progress:\
*Cryomirror:\
***We have more delays in the cryogenic mirror mount, in part due to
furnace problems

• We have a new cooling setup where the output cryogen is
subcooling before it is brought vapor.  We plan to test it later today
or early next week.

***2.8 micron mirrors: ***

3\" dia OC mirrors for use with the 2.8 um wiggler are in fabrication.
We now have on hand the 2\" dia HRs and OCs, as well as the 3\" dia HRs
for this configuration. We mounted a 2\" OC mirror that is figured to be
used with our existing cavity and wiggler configuration, checked to
confirm it still met specs, then installed it yesterday.

***Scraper outcoupler:***

No additional work scheduled in the near future.  We are devoting time
to analyze the results, and compare them with theory.

  

***Other activities:***

With the down period extended, we slightly expanded our scope of
activities and split work in the vault across two weeks.  This week we
concentrated on the OC assembly.  The unused 2\" mirror is now occupied,
and so it\'s LVDT wiring was fixed.  RTDs were added to better
understand the amount of power being absorbed by the mirror mounts.  The
ion pump was removed, baked, and reinstalled.  Next week we concentrate
on the HR assembly, which receives two new mirrors (6 um and 2.8 um),
the RTDs, and the ion pump maintenance.  We also plan to install a new
OCMMS (HR side) viewport assembly.

We checked out the loaner streak camera by using the pulsed (\~ 50 ps)
output of the drive laser. We prepared updated slides for Thursday\'s
Navy  review .  G. Neil gave presentations of our JTO projects at a
review held in Albuquerque.

**Terahertz:**

With the opening of the vault, the beamline support structure anchors
were installed.  There is minor interference between the ceiling support
structure and some water and sprinkler pipes.  Plans were made to move
the pipes to the side.  M1 has finished initial machining and is ready
for polishing at the vendor.  An initial meeting took place to determine
the safety requirements for operations of the beamline.  A number of
beam profile calculations were performed in preparation for a follow-up
meeting.  It is, however clear, that a second beam shutter will be
required and that this will require an additional port close to the
second diamond window.  A further minor change to the beamline that is
required is the addition of spreaders to the first bellows assembly to
take the vacuum force.