# MEMORANDUM

**To:** Distribution

**From:** F. Dylla

**Subject:** FEL Upgrade Project Weekly Brief -- February 7-11, 2005

**Date:** February 11, 2005

**Highlights:**

Our FEL operations suffered this week with problems induced in FEL
cryomodule 3 due

to last Friday's scheduled maintenance on the Central Helium Liquifier.
We should recover from these problems with a planned temperature cycle
of the module this weekend through the early part of next week. Despite
this diversion, we accomplished the following:

\- the hardware for projecting alignment laser light from the Optical
Control Room to User Lab 1 was installed and checked out so that the low
level certification of User Lab 1 could begin this afternoon.

> \- with further lasing operations at 2.8 microns using the broad-band
> optical couplers, we are observing some very interesting phenomena
> relative to the stability of hole-output coupler oscillators and the
> sensitivity of such systems to mirror figure and stigmatism errors.
> (See Steve Benson's discussion for details).
>
> \- we made good progress on the UV layout this week; the
> engineering/design layout of all beam transport hardware was completed
> and released
>
> \- we received power supplies we ordered for the upgraded sextupoles
> which will be installed in both the IR and UV systems in addition to
> the required ion pump supplies for the UV system

**Management:**

We began a serious look at the impact of the proposed FY06 budgets that
were announced this week by the Administration.

With the assistance of the Project Management Office, we completed an
analysis of the cost-performance data for both the IR and UV projects in
for the January project reports.

The DOE Site Office delivered our FY05 Inter-Agency Agreement to the US
Army Night Vision Lab for our proposed FY05 THz beam-line activities. We
hope to re-commence the activities on this beam-line in the next few
weeks when the Agreement is approved by the Army and the funds are
transferred.

We had a successful design review of the civil modifications of the FEL
Facility mechanical equipment room for the new FEL Injector Test Area.
We thank the staff

of Plant Engineering for their work on this task.

Specifications were completed for the 80 kW RF systems for the 100 mA
injector test stand. They were passed on to Procurement for the RFP from
the previously identified vendors.

The IR wiggler gap mechanism procurement was completed and awaits final
DOE approval before placement. The winner bidder meets our cost and
schedule targets.

**Beam Operations** (Steve Benson)**:**

Progress was slowed this week by a problem with the zone 3 cryomodule. 
It was warmed up inadvertently last Friday during work on the central
helium liquefier (CHL) and we had difficulty operating the first three
cavities on Monday.  We spent quite a bit of time in detective work to
find out what was causing the problem.  We finally decided that we had
absorbed gas on the first three cavities, increasing the RF losses, and
that another warm-up, this time done more carefully, was called for.  We
tried to see if we could operate at 135 MeV but found operation at that
energy too unstable.  We then backed down to 88 MeV for injector studies
and optical beamline commissioning.  On Wednesday we optimized the FEL
and studied the behavior of the laser with the hole output coupler.\
Operation of this laser with hole coupling is quite different from
operations with the transmissive output coupler.  In any hole-coupled
cavity the mode tries to avoid the hole by lasing on higher order
modes.  We found last week that the laser was doing this.  In an FEL the
higher order modes are suppressed due to their relatively poor coupling
to the electron beam.  When the gain is high however they can still lase
since the gain is high and the loss is quite low.  They can be
suppressed using an intracavity aperture or by cavity length detuning. 
What all of this means for laser optimization is that one has to be very
careful to optimize at very low current.  We found that this was
feasible since the laser was lasing far above threshold.  We could lower
the drive laser power by a factor of 8 from the nominal value and still
lase.  In addition, the turn-on time for full charge operation was less
than 20 microseconds.  This indicates that the net gain is at least
30%.  The detuning curve is consistent with a gain of approximately 30%
as well.  We did not get a chance to measure the losses and have no good
way of measuring the output coupling efficiency.   This gain is a bit
lower than what is predicted by the spreadsheet.  The cause of the low
gain is probably the astigmatism in the mirrors.  As mentioned last week
no evidence of astigmatism was seen in the optical mode even when lasing
on the higher order modes.  This is a very significant result and
deserves some theoretical investigation.\
Power optimization is very difficult with the hole coupling since any
attempt to increase the gain tends to reduce the threshold of the mode
hopping.  Once this occurs, the extracted power increases but the output
power is dramatically reduced.  By operating at low current and about
one third of the way out on the detuning curve we could get a stable 40
W output power.  Operating at higher current or charge only increased
the power slightly before mode hopping occurred.  This will be less of a
problem at shorter wavelengths where the hole is larger relative to the
mode.  We did operate at up to 60 W with no difficulty.  Some evidence
for mirror heating was seen at this power level.\
Thursday was lost to CHL problems.  Friday was spent partly doing
quantitative studies of the injector longitudinal phase
characteristics.  We are spending time this afternoon commissioning the
optical transport to User Lab 1

**WBS 4 (Injector):**

Progress continues on drawings and design modifications for our second
dc photocathode gun assembly. On Thursday another flat 6-in electrode
was SiO2-coated in the W&M\'s plasma source chamber. This electrode will
be mounted in our High Voltage Test Stand (125 kV) next week and tested
under high voltage the following week. Today we are performing
calibrations on injector viewer ITV0F06 and the synchrotron light
monitor viewer 2F08 in preparation for longitudinal phase space injector
measurements.

Gun HVPS - The system is fully operational.

**WBS 5 (SRF):**

Progress on the 750 MHz cryounit is as follows:

\- AES is in the tuning stage of cavity fabrication for the 750 MHz
cryounit with expected shipment to JLab next week (14 February 2005).

> \- JLab & AES agree to extend CRADA to complete end can fabrication.
>
> \- Warm-to cold beam-pipe preliminary drawings sent to JLab CASA for
> bellows shielding analysis.
>
> \- Punch list for project completion being developed for review at
> next AES/JLab coordination meeting.
>
> \- AES is still waiting for funding authorization to be finalized;
> this is needed in order for AES to continue on with purchasing
> components.
>
> \- Cavity tuner fabrication is out for RFQ.
>
> \- JLab CASA HOM analysis in progress.

**WBS 6 (RF):**

RF - Cryomodule FL03 is being warmed-up this weekend.  It will be leak
checked, refilled, and pumped down next week while CEBAF has the LCW off
for maintenance.  FL03 is scheduled to be operational again next
Friday.  All RF systems are operational this week.

 

Specifications for the 80 kW IOT\'s and HVPS\'s for the FEL Injector
Test Stand are complete and in final approval.  Purchasing has been
alerted to move quickly on this RFP.  Several vendors have expressed
interest in this work.

 

**WBS 8 (Instrumentation):**

Operations this week was not as planned, but perhaps more of a didactic
exercise. The seriatim of events were academically educational but we
could have been more productive learning to operate a hole coupled
optical cavity than an upgraded cryomodule.\
    We are very excited about a new ability we have added to our
Accelerator-IT skillset; a system to send EPICS process variables to the
Devlore database via http requests. For a while now we have been
considering how to solve the problem of closing the loop between the FEL
design model (aka Dave\'s XLS spreadsheet on his laptop) and the current
machine configuration in EPICS. Our solution has opened up more
capabilities that we had hoped for. Without adding any external
dependencies to our \'very\' autonomous accelerator controls system, we
are implementing a very simple method for archiving the machine
parameters and performance measurement data into the configuration
control database. This function will allow us to automate the collection
of performance vs. configuration data for the FEL in any number of ways
and will also be able to respond to requests from the controls system
for stored configuration values. This closes the loop, and as a
by-product of the process, we will be able to use the Devlore
web-interface as a method of presenting an \'always up-to-date\'
interface for viewing the current status of the machine and provides
easy access to the histories of the machine values. We should have a
proof-of-principle web-page available by COB today. When finished it
will be accessible at: <http://laser.jlab.org/status>\
    Progress continues on the RF-DC Linear Converter PCB design and
documentation.  The parts have been ordered for the assembly and the PCB
order should go out for quotes next week.  The PCB\'s Carrier board
design continues while considering the various applications of these
RF-DC Converters throughout the FEL.  The Charge/Dump Current Monitor
Chassis was repaired to give the Alignment Mode Chassis the permissions
it needed to allow \"Alignment Mode\".  Planning for the chassis to be
upgraded or rebuilt, to accommodate all of the IR Beam Current Monitors,
UV Beam Current Monitors, and the dumps of the FEL is under way.\
    Several new monitors for the control room have been received.
Mounting plates for them are being fabricated with installation expected
by the end of the month. Drawings are being completed for the mounts as
well. Work continues in the control room to upgrade (& clean up)
desktops. A tray has been installed to hold the monitor power supplies. 
The patch panel going to this area has been relocated in order to
maximize desk space in the control room.  This will eventually occur for
all three work areas. New LCD TVs are replacing the old tube versions.\
    There was very productive meeting with S. Benson concerning the new
Laser Personnel Safety System (LPSS). Decisions were made on changes to
the MEDM screens and the modes of the user labs associated with lab
safety. We\'re working with Al Grippo on the implementation of the Omron
to EPICS driver for the LPSS. Now that we are able to bring light
upstairs, we spent some time this week dusting off the \'Alignment Mode
Permit Chassis\' and ensuring its proper operation to the LPSS master in
the optics control room (OCR). The Alignment mode permit chassis looks
at both the RF bursts coming from a current cavity as well as the 1G
dump current and determines if the established Alignment mode laser
criteria duty factor and maximum macro pulse width) are satisfied. There
was a discussion about calibrating the threshold setting for the minimum
current required for lasing, but Steve informed us that the lasing
threshold setting that we used for the IR-Demo was still appropriate. In
addition to this work, there was some external debugging required of the
charge/dump current monitoring chassis, but having done that, the
alignment mode permit chassis/system is ready for light.\
    The WesCam software was updated for some requested changes in its
mode system. There will now be a mode that does not trigger off the beam
sync. The IOC reboot and the software upgrade will occur next week
during the down.\
    All of the 6 kwatt Sextupole power supplies and the 38 channels of
(Varian Dual Controllers) ion pump power supplies were delivered this
week. Installation activities for the UV upgrade are beginning to step
up with the rack design and layout in Zone 5 for the placement of these
14 Xantrex 6 Kw power supplies and controls chassis\'s. These PS will be
used on the UV Sextupoles. Planning of the AC power, rack cooling and DC
power to the magnets have also begun.\
    Construction continues on the THz hutch in Lab 3. The layout and
design for the Terahertz hutch in Lab3 is complete and fabrication has
begun. The extruded aluminum parts are being cut (machined) to the
proper length. Limit switches and interlocked valve power were installed
for the insertable beam dump in Lab 1. Low level commissioning of the
LPSS for Lab 1 should be complete by close of business this week. Check
prints for the FEL High Power Dump Mux box were received from EECAD and
re-submitted for final documentation. The Mux box was installed, cables
terminated and commissioned in FL08.

**WBS 9 (Beam Transport):**

***Sextupole (SF)***

•   Fabrication is continuing at New England Techni-Coil. Materials
remain on order. Design of the winding form is starting.

***Replacement Chicane Dipoles GW)***

•   Fabrication is continuing at New England Techni-Coil. Steel for two
of the four magnets will be heat-treated this weekend in anticipation of
finish machining start next week. Winding the first coil started. Field
clamp machining started.

***UV Line***

•   Position and number of diagnostic elements were verified on the
layout with ten shifts to new positions or local reconfigurations for
assorted reasons. Vacuum roughing valve zones and their Pirani Gauge
positions as well as the Cold Cathode gauge positions for fast valve
protection were solidified. We simplified some differential pump
stations to a simple Tee and a NEG pump.

• Vacuum analysis of the precise number of Ion Pumps and their position
awaits Tim Whitlatch's analysis, but we are going ahead with an
estimated position and quantity that may easily be filled in later.

• Vacuum Ion Pumps were ordered.

• With regard to our plan to regain our schedule slip, the ME Group is
starting to work its plan to utilize the resources to get the effort
done on time and in an efficient manor.

• DULY Research has started to magnetically model the conversion of the
SC sextupole to the SS sextupole. No results to report

• The faster PC workstations are late by a week

• The statement of work to send the dipole chicane stands and vacuum
chamber to an outside firm for design was checked and the requisition
signed.

•   Design of the upstream corner chamber was almost complete and layout
of the opposite corner was started.

***Injector Multi-slit upgrade***

• The fine slot paddle parts were delivered today.

***UV Wiggler Progress***

•   

**WBS 10 (Wiggler):**

All details have been worked out with the prospective vendor for the IR
wiggler gap mechanism.  The package was sent to DOE for approval.  With
that approval we can award the contract.

The UV wiggler outline drawing was placed into a layout drawing along
with the vacuum chamber cross-section of the Argonne Lab Wiggler A's.
Argonne will be sending us the details of the chamber drawing so that we
can begin design. In the mean time, the stay out zone drawing that will
accompany the request for proposal for the gap adjustment mechanism was
started.

**WBS 11 (Optics):**

***2.8 and 1.06 micron mirrors: ***

Our attempt to mount a mirror using a new adhesive did not work well. 
We had a pure astigmatic distortion.  Discussions with the vendor were
quite useful, and we are following their suggestion.  In the meantime,
we are preparing for the open period that begins next week.

 ***Other activities:\
***This week was devoted to the installation of components that will
bring FEL beam into User Lab 1.  We once again learned that nature
abhors a vacuum; with nearly every swaged fitting we made up leaking. 
That behind us, the optical beamline is now contiguous to User Lab 1. 
We plan on doing laser beam characterization (mode size, distribution,
jitter and drift) at 2.8 microns later today.  We are continuing our
work on delivering beam to other labs with the purchase of GaAs wafers
(for harmonic filters) and beam modeling.

Other work this week has been devoted to preparation for next week\'s
installation.

We assisted with the injector studies with measurements of the bunch
length using the streak camera.

## UV FEL

We are poised to do measurements on the beamline viewer from I&C, once
we get through some other time-critical work.  We received a second bid
on the vacuum vessel bake-out jackets, and are proceeding towards
granting an award.  We are zeroing in on the anticipated absorption
(both from the coating and substrate) of the sapphire mirrors we\'ll be
using at 350 nm as well as at the 2nd and 3rd harmonics, and this is
being used as better input for the analysis effort on the cryogenic
mirror flow parameters.  The Mechanical Engineering Group has completed
a complete schedule of resources needed to complete the optics tasks,
and are preparing bid packages for the hardware that is identical to the
IR Upgrade.