MEMORANDUM
To: J. Albertine, D. Helms, W. Skinner
cc: Division (M7), FEL Coordination Group
From: F. Dylla
Subject: IRFEL Weekly Report November 18-22, 1996
Date: November 22, 1996
Management
The project financial reports were prepared for the October monthly
report which is planned to be released next week.
Preparations continued for three major upcoming meetings: the
SURA Maritime Technical Advisory Committee meeting on Dec. 17-18,
the LPC Workshop on Jan. 21-22, and the DOE FEL Review on Feb.
25-26.
A colloquium was presented at Argonne National Laboratory on Nov.
22 on the subject of materials processing with high average power
light and the FEL development program at Jefferson Lab.
A first draft of technology timelines leading to a MW-class FEL
was prepared, and it will be refined in the coming weeks as part
of the preparations for the upcoming meeting of SURA's Maritime
Technical Advisory Committee.
Injector Test Stand
Regarding operation of the 250 keV gun:
We made several transverse-emittance measurements with the laser
beam displaced off-axis on the photocathode. These measurements
were done to test the viability of running the FEL using off-
axis portions of the photocathode to reduce the number of recesiations
and thereby improve the overall availability of the gun. Preliminary
results indicate that the emittance varies significantly as the
laser beam is moved across the photocathode. We have initiated
numerical simulations to understand the mechanism.
We took three more sets of publication-quality data using the
4-mm-diameter, 2-mm-diameter, and 1-mm-diameter apertures on
the laser beam. We then recesiated the photocathode, once again
achieving a quantum efficiency of 4%, and resumed taking data.
Regarding fabrication of the new high-voltage stack:
All three ceramics (Serial #1, #6, and #2, in that order) have
now been sprayed a second time in an effort to drive their conductivities
to a range where we are sure the field-emitted current will drain
off and the uniform gradient will not be altered excessively.
The vendor in California has had a difficult time taking reliable
measurements to determine if their resistivities match. The measurements
are sensitively affected by atmospheric conditions, and they have
been complicated by rainy weather and a damp atmosphere. At week's
end a retest of #6 after heating in an oven and purging with dry
nitrogen showed that its resistivity matches that of #1 to within
20%, an improvement over the previous test which showed a 100%
difference. We are assessing whether to do a final qualification
test using vacuum facilities here at Jefferson lab prior to brazing
the rings.
Regarding other progress, we decided to ship the rotisserie for
ion implantation to LBL and sent it by air freight. The new mid-voltage
ring for the stack is being polished at 9 micron diamond grit
on one shift. The samples of ion-implanted aluminum oxide coupons
provided by LBL need to have come conductive paths on their edges
removed by bead blasting.
Regarding testing of the injector cryounit:
Data reduction for the cryounit test was completed. The data
support a nominal operating point for which the accelerating gradient
of the first cavity the electron beam sees is 11 MV/m, and the
accelerating gradient of the second cavity the beam sees is 9
MV/m. These are consistent with earlier testing of the cavity
pair prior to its installation in the cryounit's cryostat. However,
the temperature profile in the waveguide deviated somewhat from
predictions, and this detail will be monitored in future superconducting
rf tests for the FEL.
Accelerator Systems
A punch list was compiled to enumerate the few details that still
need to be resolved prior to a formal freeze of the top-level
machine drawing. Conceptually, the most important detail is a
slight revision of the second recirculation bend to make it more
compatible with upgrade paths and thereby reduce the work that
will be necessary to reconfigure the machine whenever future upgrades
are done. We anticipate being able to institute the freeze by
mid-December, at which time we will establish a change-control
process for the overall layout. The change-control process for
the diagnostic suite is already in effect and continues to work
smoothly.
The design of the IRFEL cryomodule was updated based on test results
of the cryounit.
A thorough test of the low-level rf system for the IRFEL took
place on 21 November on the main machine at the South Linac 21
location. The test was very successful, resulting in a short
punch list containing only minor hardware modifications.
We recently modified the specifications of the power supply for
the 8 kW klystrons to make them more compatible for installation
and use in the FEL Facility. The procurement package is back
on the street. We have given the vendors a short time to respond.
The rf racks for the IRFEL arrived this week.
The process of carrying out an internal review of the design of
the dipole magnets commenced. Some of the specifications needed
to be solidified based on new data relating to suppression of
fringe fields in the prototype dipole. A staff member traveled
to Northrop Grumman to finalize details of their design of the
optical-chicane dipoles. The plan is to close out this review
hopefully next week, but at latest during the first week of December.
Quotations on the coil assemblies for the weak-field quadrupole
magnets were received and are being evaluated. Fabrication of
the prototype trim quadrupole was completed. The contract to
fabricate the core of the prototype sextupole magnet was awarded,
and we are expecting to receive it by mid-December.
Detail drawings of the injector vacuum pipe neared completion
and are undergoing a final evaluation of impedances. Cable tray
and utility layout is nearing completion.
Work has continued to characterize the expected performance of
beam-position monitors around the IRFEL in preparation for an
internal design review. In view of schedule conflicts, we slipped
the review date from 22 November to 27 November.
The Software Group put together a detailed design of the configuration
of computer hardware and networking that is needed to control
the IRFEL, to include specifications and cost estimates.
FEL Systems
Wiggler
A meeting was held to settle the design of the wiggler support
at the 85%-level. This is preparatory to ordering the optical
bench. We are in the process of developing the specifications
for the vacuum chamber and its support.
Optics
We ordered more diagnostic equipment (e.g., a power meter, infrared
detectors) and more catalog items for the optical cavity, such
as the alignment He-Ne lasers and the linear translation stage.
We are requesting new quotes on optical transport mirrors, as
we are now interested in getting gold- (instead of silver-) coated
optics to cover the full range of expected wavelengths. Our intent
is to order these mirrors next week.
Operations/Commissioning
To date, procedures have been written for single-pass commissioning
of the IRFEL hardware from the gun through the cryomodule and
into the energy-recovery dump. From here, the process will continue
as we work our way to the straight-ahead first-light dump and
then through the recirculation pass.
Facility
Work on the interfloor area continued with gravel being placed
in the entire floor and approximately 1/3 of the area covered
to height with sand. Penetration tubes were placed and cut to
length in the filled area. Positioning of the lights in the tunnel
was readjusted based on the latest layout information. Wiring
was begun in the tunnel. The filling and layout of the loading
dock and lobby area continued as did the truck ramp retaining
wall layout.
We continued working on the layout of the injector in the FEL
Facility, and we resolved interferences with lights. The budgetary
quotes for the 600 kV power supply tank came back and are within
budget. Minor changes are being made to the drawings, then we
will prepare the final bid package and get the final quotes.
Delivery is expected in 12 weeks. We received one bid for the
new clean room at a price of 75-90 k$ and are still waiting for
an estimate from the vendor who built the clean room in the Injector
Test Stand for 39 k$.