MEMORANDUM
To: J. Albertine, D. Helms, W. Skinner
cc: Division (M7), FEL Coordination Group
From: F. Dylla
Subject: IRFEL Weekly Report Jan. 13-17, 1997
Date: January 17, 1997
Management
Preparations were completed for the LPC workshop which will be
held next week on Jan. 21-22. The agenda and charge were finalized
for the DOE-BES review to be held on Feb. 23-24. Commitments
were obtained for the external reviewers.
In view of the slippage in the fabrication of the new HV for stack
assembly, the photocathode gun, coupled with our commitment to
install the IRFEL in the FEL Facility by 30 Sept. 97, we formulated
a contingency plan that preserves both the schedule and technical
content of the Program. The central idea is, if necessary, to
delay complete debugging of the injector until after its reinstallation
in the FEL Facility. This saves time because it avoids a duplicity
of 10 MeV commissioning activities, i.e., in both the ITS and
FEL Facility. The resulting schedule accommodates two important
global concerns. It employs Jefferson Lab manpower when it is
available for the reinstallation activity, namely during summer
1997. It also gives us a reasonable chance to meet the Dec. 97
first-light milestone.
M. Owens and M. Cardarelli, of the defense staff for Senator Robb,
toured Jefferson Lab and the FEL Facilities on Jan. 16.
Injector Test Stand
ITS activities have been oriented toward resuming operation of
the gun at 250-300 kV. A new wet-etched GaAs wafer was inserted,
and we are working on recharging the cesiator to "convert"
this wafer into a photocathode. Preparations to bake the gun
and beamline continued. We estimate restarting the gun during
the first week of February.
Regarding upgrading the photocathode gun:
* Cr/V-Oxide-Coated Ceramics - Last week's report on the Cr/V-oxide-coated
ceramics was garbled and should have read as follows: We discovered
a glitch with the apparatus recently used to measure the coating
resistances of the coated ceramics in vacuum. The result was
faulty readings that indicated artificially high coating resistances.
After correcting the glitch, subsequent measurements revealed
coating resistances on the order of 5-6x10^11 ohms on two of the
ceramics. At these resistances, the maximum current the coatings
can conduct to ground is projected from the data to be about 0.6
µA. However, this drift current is too low, in that calculations
project the field-emitted current from the cathode support tube
to be in the µA-range at 500 kV. Assuming the coatings were
to conduct this level of field-emitted current to ground, the
result would be considerable distortion of the voltage gradient
across the ceramics. We estimate that coating resistances below
1x10^11 ohms will result in drift currents that are high enough
to keep the voltage distortion acceptably low. On the other hand,
coating resistances need to be >5x10^9 ohms to keep the drift
current low enough to prevent unacceptably high joule heating
of the coatings. In short, we are trying to achieve coating resistances
in the range 0.5-10x10^10 ohms. Plans are to decide what to do
with these ceramics after we have the ion-implantation results
from LBL.
* Coated Cathode-Support Tube - FM Technologies is calibrating
their apparatus with a short stub of polished tube that we sent
them, and they claim to be on schedule.
* Ion-Implanted Ceramics - Lawrence Berkeley Lab coated the "dummy"
ceramic to a dose of 5x10^16 per cm and obtained a resistance
of 6x10^11 ohms. The process is successful and shows good potential
for achieving coating resistances in the desired range of 0.5-10x10^10
ohms. Plans are to refine the process and implant two of the
improved ceramics over the next several weeks.
Accelerator Systems
Regarding the beam-transport system:
With continued testing of the prototype dipole magnet, coupled
with Northrop Grumman's continuing work on the designs of the
recirculation dipole magnets, we are on the verge of initiating
procurement of the optical-chicane dipoles. Associated with this
activity, we have scheduled the closeout of the Dipole Magnet
Review for next week, 22 Jan 97.
Concerning other beam-transport developments -- All commercially
available components for the vacuum system are on order. We have
started to develop procedures for cleaning and installing the
vacuum system. Design drawings of the stands and girders for
the quadrupoles in the back leg of the beam-transport loop were
signed off. The main vendor for the quadupoles received the necessary
tooling for winding their coils. We are now putting more emphasis
on the beam- transport system needed for first light, for example,
the design process leading to the injection and extraction dipoles.
Regarding cryomodule fabrication:
We continue to have problems with cracking of ceramic warm windows
during testing, and a team of people continues to work vigorously
to find a solution. As one potential solution, a warm-window
assembly is about to be tested, starting today (17 Jan), that
incorporates massive stainless-steel flanges with reduced metalization
geometry. In parallel, we have Northrop Grumman engineers looking
at window-heating issues, and a SLAC visitor is coming on 27 Jan
to consult on windows.
Stainless-steel higher-order-mode (HOM) subassemblies were qualified
and delivered. Two assemblies have undergone final brazing.
Test and evaluation of final assemblies has started and should
conclude on 22 Jan. Additional HOM assemblies are in brazing,
with completion of two scheduled for 24 Jan.
Regarding electron-beam diagnostics:
The final meeting of the Beam-Position Monitor (BPM) Review Committee
took place. Plans are in place for timely delivery of the baseline
suite of BPMs. The beam-diagnostics group also has some ideas
for alternative BPM calibration methods that, if viable, would
help shorten the schedule and save money. They will explore these
ideas on the side, an activity that will not affect the procurement
schedule. One challenge for the procurement process is to find
a vendor who can fabricate and deliver the BPM suite on a 60-day
contract, which is shorter than the norm of 90 days. The search
is beginning. There are some other actions from the Review.
They include testing the revised prototype stripline BPM, which
we received from the machine shop this week, and completing a
set of thermal analyses of the BPM designs, the results of which
may influence some operating procedures. A memo is in writing
that will formally close out the Review.
FEL Systems
Wiggler
Drawings are complete for the wiggler supports, and a meeting
was held with Northrop Grumman to finalize the vacuum chamber
and its supports. No special problems have been identified.
Manufacture of the wiggler is proceeding on schedule. All poles
and machine parts have been received. Magnets are due in Feb.
97.
Optics
The machine shop finished fabrication of the mount for the Brewster
pickoff for the injector drive laser. Installation of the mirror
is in process. Modifications were made to the optical support
bracket drawings based on the actual dimensions of the optical
mounts. Some of the mount brackets for the optical cavity have
been finished. Machining of the rest of the optical mount for
the FEL is proceeding well.
Optical components are being received on schedule from the vendors.
In a parallel effort all fasteners, etc. are in order. The first
iteration on the revision of the optical transport can is drawn
and under review. Draft layout of the optical transport in the
lower level of the FEL Facility is complete and under review.
Initial computer communication using the EPICS control system
was established with the LVDTs used to readback mirror position.
This is a major step toward getting computer control of the optical
cavity. In a phone conversation with S. Siahatgar and H. Bennett,
plans were reviewed for a bench test of the stability of the optical
cavity.
Operations/Commissioning
As discussed above under "Management", we formulated
a contingency plan and schedule for development/commissioning
of the IRFEL injector.
Facility
A significant step forward occurred this week when the second-level
floor was poured. This enclosed the interfloor piping and set
the stage for construction of the girder framing on the upper
floor. However, continued wet weather prevented completion of
the building berming required for BOD1. Work continued in the
linac vault to mount piping and electrical systems on the walls.
Surveying continued to determine the as-built positions of the
Facility elements. Construction of the framing for the entrance
way and loading area is well underway.
The monthly meeting was held with the contractor to review status
and future schedule. It now appears that the contractor will
miss the second BOD by approximately 2 weeks due to delays in
receiving the framing structure for the second floor. We are
now replanning the installation of the FEL equipment racks to
minimize delays due to this slip. One approach which will help
has been adopted: phased installation, east-to-west, in the upper
level based on drywall completion.
A request for bids is out on both the fabrication of the high-voltage
power supply for the FEL Facility's 5 mA photocathode gun and
the installation of the Facility's clean
room.