MEMORANDUM
To: J. Albertine, D. Helms, W. Skinner
cc: Division (M7), FEL Coordination Group
From: F. Dylla
Subject: IRFEL Weekly Report, May 19-23, 1997
Date: May 23, 1997
Management
The photocathode gun was successfully baked this week, allowing
gun operations to resume next week. With the schedule slip caused
by the need to replace the cathode in the gun and one of the warm
windows in the cryounit, options for a revised ITS schedule were
examined this week. We have a firm date for placing the cryounit
in the FEL Facility by July 1 for cryogenic testing. We need
to work out the last possible date of having the gun and the RF
systems consistent with maximizing gun test time and using the
installation labor as efficiently as possible.
The monthly report for the IR Demo project for April 1997 was
distributed on May 22. Earned-value cost and schedule variances
continue to grow until we can take credit for magnet deliveries
by mid-summer and the recent shipment of the wiggler (pending
resolution of the shipment problem noted last week).
Preparations continued for the two major project meetings in June:
the second MTAC meeting on June 9-10 and the next LPC Workshop
on June 25-26. A preliminary agenda and travel logistics were
distributed to MTAC on May 20. Comments on the preliminary agenda
were received from the MTAC chair, Adm. Baciocco, and J. Albertine.
Speakers are being identified for the LPC Workshop.
At the second Virginia Technology Summit, held in Richmond on
May 21, the FEL Program was given high visibility in presentations
by Senators Robb and Warner, the two gubernatorial candidates
from Virginia, and from the group leader for a task force on high-performance
manufacturing initiatives.
Injector Test Stand
Regarding the photocathode gun:
Bakeout of the gun was completed. The gun was then reassembled,
NEG pumps reactivated, NF3 recharged, SF6 tank and high-voltage
(HV) cable reinstalled, and SF6 recharged. We started HV processing
Thursday morning, 22 May 97. We are taking the gun to 420 kV
for 12 hours as was done last week, and then will do a 20-hour
cathode heat-cleaning cycle at 580 C. This will be followed by
manufacture of a cathode Sunday or Monday after the cathode area
has cooled sufficiently. This should allow field-emission measurements
Tuesday, May 27 after which operations with beam would ensue.
Cursory examination of the cathode under a microscope revealed
that it was "frosted" (the arsenic was vaporized out
of its surface). This was probably caused by heat cleaning at
too high temperature when we were attempting to heal the field
emmission sites observed last week (we went near 700 C). That
is why we are going back to our standard backout temperature of
580 C. At this time, we still do not know definitively what was
causing the field-emission problem reported last week although
etching caused by the removal of arsenic could certainly lead
to field emmission sites
Regarding the cryounit:
Except for the Cavity Window Temperature (CWT) alarm, the interlock
checks have been completed for the cryounit in preparation for
planned testing with warm windows. The cryounit is presently
warm and must be cold in order to set the CWT alarm. We found
that the new spare 50 kW klystron has a loose input connector
and cable. We contacted the vendor about the problem, but have
yet to hear back from them. If need be, we will contact them
again next week.
Regarding development of warm ceramic windows for the cryounit:
In view of the string of recent difficulties with the development
of robust warm ceramic windows, and in view of the short schedule,
we reformulated our development plans. The earliest date for
having two ceramic warm windows qualified for installation and
subsequent testing in the cryounit is June 14, which may or may
not (probably will not) leave sufficient time for the tests prior
to moving the cryounit to the FEL Facility. If not, then we will
do the remaining tests of the cryounit in the FEL Facility. A
synopsis follows.
Short Term: Produce six 50 kW RF warm windows based on the existing
design. They have performed satisfactorily under "normal"
operating conditions. Failures encountered in the most recently
produced warm windows are attributed to off-normal operations
that led to run-away conditions, depositing extreme amounts of
RF power into the windows.
Scheduled activities are:
- Complete by May 29, 1997: Prepare in house flanges for e-beam
welding.
- Complete by June 2, 1997: Remove Japanese ceramic from flange
(e-beam weld leaked) and reprocess it, to include removal of nickel
foil, metalization of ceramic, and characterization of ceramic
in resonant ring. Select four lowest-loss ceramics from existing
inventory, send them out for metalization (along with Japanese
ceramic), and characterize them in the resonant ring. Fabricate
two additional flanges to increase throughput of window fabrication
and rework.
- Complete by June 5, 1997: Braze five nickel eyelets to ceramics.
- Complete by June 6, 1997: E-beam weld five ceramics into flanges
and leak check.
- Complete by June 10, 1997: Resonant-ring-test five window
assemblies to 50 kW in air.
- Complete by June 14, 1997: Test two windows in vacuum fixture
to 50 kW. - Complete by June 18: Test two windows in vacuum
fixture to 50 kW.
- Complete by June 23, 1997: Test two windows in vacuum fixture
to 50 kW.
Medium Term: Two medium-term programs are ongoing to provide
alternative solutions for RF warm windows. (1) The BeO Northrop
Grumman windows -- Ceramics are in-house, flanges are in production,
and final assemblies are due to be completed at the end of June.
(2) Redesign of Jefferson Lab windows -- The design uses a thin
wall, water cooled, copper waveguide support for the ceramic braze
joint. Ceramics have been ordered from Wesco and will be ground
locally. Prototype assemblies are expected in August 1997.
Back-Up Plan: Enhanced polyethylene windows -- Cooled polyethylene
windows could have an extended power limit to allow for operations
at ~ 10 kW. The existing polyethylene window is rated for 8 kW
and is borderline for FEL first light. Cooling can be incorporated
into the exterior waveguide assembly. It would be trivial to
install and could be accomplished on a cold cryomodule. Implementation
of this would be required in Feb-Mar 98 if ceramic windows have
not surfaced beforehand. This would support first light at 1.1
mA average current and provide additional development time.
Accelerator Systems
Regarding the beam-transport system:
Procurement of dipole magnets are generally proceeding on course.
Everson Electric was having some minor difficulties constructing
the first-article optical-chicane dipole, but we are working with
them to resolve the difficulties. Designs for the sextupole magnets
are complete, and they are in procurement. The long Panofsky-style
trim quadrupoles are out for bid.
We completed measurements on the mu-metal air-core corrector magnet
to quantify saturation and hysteresis effects. There were no
signs of saturation, a favorable finding. However, there is nonnegligible
hysteresis. In light of the hysteresis data, we are in process
of determining where along the machine these correctors could
be used.
As reported last week, we also are having another prototype air-core
corrector built by Syntronics. This vendor supplies magnets based
on a choke-coil design for medical imaging, an application that
requires magnets having inherently low harmonics, and therefore
high field uniformity. Thus, this design seems like a good candidate,
and we may be able to modify the prototype in-house, if needed,
in conjunction with measuring it.
The design drawings of the vacuum chambers for the optical chicane
are complete. Welding on a six-foot-long, trial square vacuum
chamber has begun, from which lessons learned will be used for
the X and Y chambers which are ready for fabrication. Northrop
Grumman continues to make good progress on the arc vacuum chambers.
Back-leg girders are being assembled and readied for installation.
We made good progress on the assembly drawings for the optical
chicane and first-light beam line. Drawings of the final girder
for the injection line were finished. Check prints will be available
on the beamline just upstream and downstream of the cryomodule
next week. Preliminary work has begun on the first-light dump
stub. The first-light dump is being fabricated in our Machine
Shop. We also made good progress on the insertable dumps (Faraday
cups).
Regarding cryomodule fabrication:
The two remaining cavity-pair assemblies completed testing in
the Vertical Test Assembly. Both passed their RF performance
criteria and are in final leak check prior to turn-over for assembly
in their respective cryounits. Cryounit #1 is complete and turned
over for assembly into the cryomodule. Fabrication of the second
cryounit is progressing on schedule. In general, the schedule
for cryomodule assembly remains tight but feasible.
Regarding electron-beam instrumentation and controls (I&C):
Upon closer inspection, there was some question about whether
some of the repaired welds of electrodes to the chambers of the
stripline beam-position monitors (BPMs) were sufficiently robust
to preclude intermittent shorts. Consequently, we decided to inspect
more carefully using a borescope and to hit again some of the
more dubious welds with the e-beam welder. Though the e-beam
welding has been challenging, it seems generally to have worked.
Moreover, there was some concern about how to clean BPMs prior
to incorporating them into assembly of the beamline girders.
We decided to clean them with acetone and alcohol in an ultrasonic
cleaner, followed by drying with a clean, dry gas, and then bagging.
We are close to turning over 13 BPMs for assembly into the back-leg
girders.
The cable pull from the Machine Control Center to the FEL Facility
is complete, and all of the fiber-optic connections have been
made and checked. The Hewlett-Packard servers have arrived and
will be installed in the FEL Facility as soon as power is available
(in about two weeks). The networking hardware is in process of
being installed.
The racks in the equipment gallery and in the control room of
the FEL Facility have been moved into position and are being wired.
Documentation of I&C activities on www continues to progress.
Regarding RF systems:
Hipotronics, the vendor for the 225 kW variable power supplies
that will drive the cathodes of the 8 kW klystrons powering the
cryomodule, is now assembling the first unit. They expect to
start testing it next week, and we might be able to witness acceptance
testing as early as the following week. If all goes well, they
could ship the first unit about June 9.
FEL Systems
Injector Reinstallation
All components for the injector crane rail are on order. Delivery
and installation in scheduled for next week. A new air handler
unit has been located by Clean Air Technology. It will be installed
after the rest of the clean room. Work on the clean room is still
scheduled to start May 28. Design work continues on the drive
laser optical transport.
Wiggler
A preliminary dimensional check of the wiggler indicates no problems
with the vertical alignement of the jaws (this is the direction
which would be affected by a vertical drop). Measurements of
the fiducials to gauge the longitudinal alignement will be carried
out next week. The machine shop has succeeded in making wiggler
vacuum tubing with the proper cross section and flatness. Welding
of test pieces is scheduled for next week. All the remaining
drawings for the wiggler vacuum chamber and the assembly drawings
for the wiggler girder were signed off.
Optics
We received 5 micron mirrors from Rocky Mountain Instrument this
week (two months early) and will ship them to China Lake for testing
(reflectance and scattering, ROC, figure, roughness). The 3 micron
mirrors (from Research Electro-Optics) are being coated this week,
and we expect them in several weeks. Some of the calcium fluoride
windows used in the optical transport system also arrived. Designs
for items mentioned last week are progressing. We are nearly complete
with a design for enclosures that will permanently surround the
optical cavity assemblies and minimize dust in their vicinity.
The bellows assemblies have gone through two of the three steps
required to be brazed to the cooled mirror holders. The optical
table that will be installed in the new clean room arrived and
was placed on the second floor of the FEL building. Several of
us attended the Exhibitor's Show at CLEO and met with current
(and potential) vendors of optical equipment including the drive
laser upgrade.
Commissioning/Operations
Detailed plans were formulated for the content and manning of
upcoming gun experiments. The content is essentially unchanged
from earlier plans that had been postponed due to the latest field-emission
problems. However, there is uncertainty whether it would be prudent
to spend the time necessary for executing all of those original
plans, i.e., to characterize the longitudinal and transverse beam
properties at bunch charges pertaining to "zero current",
first light, and full-power operation, then to look at photocathode
lifetime, performance at higher voltage, performance at other
bunch charges, etc. We will decide on priorities as we see how
well the latest gun configuration works.
The newly configured gun includes the cathode-anode spacer for
lower cathode-stand-off voltage, which means the simulations for
full-current beam from cathode to wiggler need to be redone.
We already have some results for the first-light beam from earlier
efforts, and have initiated the full-current study.
Having settled on an overall commissioning process, we made a
first cut at defining commissioning "teamlets" to turn
on various IRFEL systems. This is one of the first steps in lining
up necessary manpower, an effort that will evolve continually
in the coming months.
Facility
Progress on the FEL Facility continues to be rapid. The glass
for the sky light and front entrance is complete. The tile in
the equipment gallery has been delayed due to illness, but it
should be completed soon. Fibercast piping for low-conductivity
water (LCW) between the FEL Facility to the south access building
is being finished. This will be connected to the CEBAF LCW system
for clean up over the long weekend. The survey crew continues
to place stands in the injector and linac areas. The magnet stands
for the optical- chicane and wiggler supports are being grouted.
Utility work in the control room is nearing completion. Drywall
in both bathrooms is complete and ready for painting. Drywall
in the upstairs lobby is nearly complete. Work began on the elevator
this week. The shaft sleeve has been prepared and inserted, and
the remaining work should take about 2 weeks. All of the transformers
wiring is complete. Wiring to most wall outlets is in place but
not yet terminated. The bulk of the AC power should be available
by the middle of next week.
Progress on the cryogenic system is proceeding on schedule. We
have now completed welding and leak testing of the 2K liquid-helium
supply and return circuits all the way from the Central Helium
Liquefier to the injector location in the FEL Facility.
The beams for the injector cranes have been ordered, and the drawings
should be completed by COB today (May 23). Plans are being made
to load-test both overhead cranes.