MEMORANDUM
To: J. Albertine, D. Helms, W. Skinner
cc: Division (M7), FEL Coordination Group
From: F. Dylla
Subject: IRFEL Weekly Report, March 3-March 7, 1997
Date: March 7, 1997
Management
Excellent progress was made this week on RF windows, new ceramics
for the HV stack assembly for the gun, magnet procurements and
the accelerator vault in the facility. Details are given in the
report that follows.
We received a draft of the reviewers' report from last week's
DOE-BES review. The draft report is positive. D. Helms and F.
Dylla visited the BES program office on March 6 to discuss follow-up
activities resulting from the review. The primary follow-up activity
is generating research proposals from the pro-positive FEL user
community to be sent to BES for evaluation. Outlines of four
such proposals were presented to BES to initiate the proposal
process.
A draft proposal and statement of work for the 1 micron IR FEL
Demo Upgrade were prepared and sent to the Navy High Energy Laser
Office for comments.
R. Li attended a workshop on March 6 hosted by the Naval Post
Graduate School on the subject of coherent synchrontron radiation.
M. Shinn gave a presentation entitled, "The Free Electron
Laser, a Possible Tool for the 21st Century Automotive Industry"
at the Automotive Laser Applications Workshop '97, held in Novi,
MI.
Injector Test Stand
This week we performed a set of magnet sensitivity studies to
investigate the relationship of the gun solenoid field to beam
emittance, particularly in the region around 20 pC/bunch. The
data suggest a strong sensitivity for emittance to solenoid strength.
The data has also been passed to the modeling effort for explanation.
We continued development work on the bunchlength and longitudinal
emittance measurement programs. In beam tests we performed several
bunchlength measurements using the rf cavity. The measurements
give a one sigma bunchlength of 20 to 25 psec. This is very comparable
to the 20 to 30 one sigma pulse width previously measured for
the drive laser pulse.
In hardware improvements we closed the feedback loops on the phase
and amplitude for the rf cavity and switched the laser to run
off the common master oscillator.
The drive laser feedback loop for phase has been closed but still
has a large RMS error. We also installed the second Conoptics
electro optic modulator which will allow us to use the gating
and timing system originally designed.
The newest version of the divide-by-two EO modulator is installed
and so far has handled full IR power (~ 20W) without problems.
We are still optimizing it. In addition, we received the new
EO modulator that will give us more flexible pulse selection.
It is installed in the beamline and is being optimized as well.
This system will allow us to also pulse the rf in the cavity to
higher gradients without going into thermal runaway. The higher
gradients will enhance our resolution for the bunchlength measurements
without sacrificing the signal to noise ratio caused by the extinction
ratio of the drive laser modulation system.
The new Ion Implanted Ceramics, having a resistance of 1.88E10
and 1.72E10 Ohms (matched to within a resistance of 10%) were
received from Lawrence Berkeley Lab. This implies a dissipation
of around 3.5 watts at full voltage of 250,000 V which is ideal.
We plan to weld the Cathode Support Tube to its flange and weld
the ceramics to their respective vacuum flanges and mid voltage
ring next week and complete the refurbishment of the Gun in two
weeks.
Also planned is the exchange of the vacuum valve between gun and
beam line and the addition of a single Multi-slit element to allow
testing its properties. The first tests are planned in about
a month after the vacuum bake out and the reinstallation and check-out
of the beam line instrumentation.
The back-up ceramic was sent from Hitemp and to Lawrence Berkeley
Lab for its implantation.
Accelerator Systems
RF systems:
The spare 50 kW klystron tube has developed a vacuum leak. The
tube will be removed from the test set and returned for repair.
Also sent out for repairs was a ITS buncher temperature sensor
card.
The chopper cavity was operated in both cw and pulsed mode with
beam this week. The bunch length measurement was run with 40
W cw into the chopper.
An interference was discovered at the legs of the new gun high
voltage power supply tank. We decided to shorten the elbow to
allow clearance.
The second high power klystron was configured to use for high
power testing of RF windows so that performance of the RF windows
can be verified before installation on the unit. An SOP for this
testing was implemented.
Hipotronics (vendor for the 225 kW power supply) is now about
2 months late. They are still claiming to be able to deliver
in May but we are concerned. We are planning a trip to the factory
late next week for a first hand evaluation.
Instrumentation and Controls:
All shielded and unshielded beam viewers were received; they are
undergoing QA checkout. Three will be connected to an RGA to
check cleanliness; the first was reviewed and looked fine.
48 of 150 vacuum gate valve control cards have arrived ready for
testing. The balance will be shipped today (3/7). The majority
(125) of these are for a CEBAF upgrade.
All 50 beamline ion pump control cards are here and being tested.
Ion pump power supply fabrication continues, the new log amp board
prototype has been tested and checked out OK. 400 of these will
be ordered; 100 for the FEL and 300 to upgrade CEBAF. The volume
purchases are helping to keep our costs down.
Beam Transport:
Design of the 180 Degree dipole and second Reverse Bend continued
at Northrop Grumman. Design of the Injection Chicane dipoles
continued at Jefferson Lab and we anticipate going out for separate
bids next Thursday.
Bids are due on the Optical Chicane Dipoles next Thursday.
Our first attempt to create the Purcell gap and glue the mu metal
on to the poles of the prototype dipole was not successful. The
epoxy was not squeezed to the anticipated zero thickness that
other tests had indicated was possible. While the adhesion proved
itself to be acceptably tenacious, we were able to remove the
mu metal and aluminum from the pole tips of the prototype with
no damage to the pole tip. We are gluing the pieces of aluminum
tooling plate under very uniform and high pressure conditions
to gain insight into the process variables before the next trial
on the prototype.
We are reviewing the layout for the required good field region
vs. the new potential stay-out zone from the edges of the chambers.
Eight weak quads were shipped from the vendor and back leg stands
and vacuum valves were received. The stands were delivered to
the FEL tunnel.
An extensive drawing signing session was held on Friday, March
7, reflecting the greater design resources available to the system
starting several month back. The drawings included the back leg
girders, Y vacuum chamber, injection line stands, optical chicane
dipole stands and quadrupole stands.
The order was placed for the two 100 A power supplies needed
for the injection and extraction chicanes with a July delivery
date specified.
Shunt construction started and system drawings of the DC power
distribution are in active production.
Cryomodule fabrication:
The second warm window was tested to 50 kW in the resonant ring
facility. Two warm windows have been assembled into the vacuum
test fixture and are being prepared for testing with the ITS 50
kW klystron. The SOP for testing with the ITS 50 kW klystron
has been written and approved. We are ready for testing when
the window fixture is completed. We expect to run rf next Monday.
Schedule for cooldown and testing the 1/4 cryomodule is set for
the week starting 17 March. This will qualify the 1/4 cryomodule
with 50 kW rf supply.
Procurements and deliveries of parts are on schedule to support
FEL cryomodule assembly. The second FEL cavity pair is scheduled
for assembly on Tuesday 13 March. This is a delay of one week.
FEL systems
Injector Reinstallation
Design of the stands in the injector is complete. The clean room
contract was awarded to Clean Air Technology. It is scheduled
to be installed by June 1, assuming that facility construction
progress is adequate.
Wiggler
All mechanical parts for the wiggler are done. The final shipment
of magnets is due next week. These will be characterized and
sorted for final assembly and testing. Final certification measurement
is now scheduled for the first week of April.
The vendor for the wiggler vacuum tubing raised their price estimate
dramatically. We are looking for alternative sources.
Optics
Efforts continue on the new design for the optical collimator.
This week the mirror mounts and the output Brewster window were
the optical cavity components being fabricated. The drawings for
the near-Brewster window assembly were signed and are in Procurement.
We began assembling optical cavity components, and have found
some discrepancies from the prints that will require some minor
remachining.
Facility
The facility this week had significant activities going on both
upstairs and downstairs. Downstairs the floor was cleaned and
sealed. Fire sprinkler pipes were hung over the full area. Placement
markers were surveyed in and established for setting the cryo
transfer line. The entrance labyrinth had wall finish work performed.
The trenches around the vault perimeter were cut and cleaned.
The ceiling was painted. After the north side was sealed the
cryotransfer lines were placed in their approximate final locations.
Several days of adjustments and survey checks will put us in
a position of being able to start welding.
Upstairs the exterior wall frames were set in place over more
than 60% of the walls. Framework was completed on the utility
area, the last major framing work required. Finish work continued
around the elevator. Roof decking was placed on about 1/3 of
the area.
In a meeting with the contractor it was determined that the floor
flatness in the lower level does not meet contract specifications.
Nonetheless it does appear possible to compensate for the out
of flatness that is observed by setting our stands at different
heights. We intend to negotiate a suitable settlement with the
contractor to compensate us for the extra effort on this item.
Current plan has the contractor completely out of the lower level
(except some testing and touchup) in one more week. This will
help our efforts to accelerate the installation activities since
we now have stands for the backleg of the accelerator, cryolines
are ready to be positioned for welding, and the cable tray is
ready to be hung as are the LCW circuits.
Operations
Discussions are underway on the details for implementing the machine
protection system. The hardware approach has been chosen and
is based on a combination of CEBAF detectors and existing Argonne
VME based detector boards. What remains to be determined is the
way in which interlocks are zoned: either based on the beam mode
in operations or geographically. Each approach has advantages
and drawbacks which will be investigated over the next few weeks
to settle on a system with the best utility.