MEMORANDUM
To: J. Albertine, D. Helms, W. Skinner
cc: Division (M7), FEL Coordination Group
From: F. Dylla
Subject: IRFEL Weekly Report, April 21-April 25, 1997
Date: April 25, 1997
Management
A number of visits occurred this week concerning existing and
potential collaborations with the FEL project. On Monday, John
Holzrichter, the Associate Director for Science and Technology,
from LLNL visited Jefferson Lab. Dr. Holzrichter directs $55M
of internally funded R&D at Livermore. The lab's work on
diode-pumped solid state lasers and ablation studies with short
pulse lasers are two projects of joint interest.
On Tuesday, Mike Kelley and his Department Head, Lewis Goodrich,
from DuPont Central Research Laboratories visited Jefferson Lab
for a briefing and tour. In addition to discussing DuPont's contributions
to the FEL program and the LPC, Mr. Goodrich had a specific interest
in the microwave technology used in the CEBAF and FEL accelerators.
On Thursday, Fred Dylla and Hermann Grunder visited the Duke
University FEL Laboratory for a tour of the recently commissioned
storage ring and discussions with university management about
collaborative efforts.
In response to questions received from the Senate Armed Services
Committee on Wednesday, a letter with supporting material was
prepared and sent summarizing the status of the present IR Demo
project, planned FY97-98 activities and supporting documentation
on the industrial support for the Demo project.
A status report on the cost and schedule performance of the project
as of March 31,1997 was prepared at the request of the HEL program
office for transmission to the Office of Naval Research.
The most important accomplishment this week was achievement of
400 kV on the photocathode gun. Experiments with the gun in the
Injector Test Stand are therefore proceeding per the present schedule.
However, the ceramic warm window in the cryounit cracked this
week, causing a setback in cryounit commissioning. We believe
we can recover and stay on the 1 Jun 97 shut- down schedule, but
it will be tight. Details are provided in the "Injector
Test Stand" section below.
Injector Test Stand
This week's activities in the ITS were marked with a notable accomplishment
and a notable setback.
The notable accomplishment is that, at 2240 on 23 Apr 97 and per
our anticipated schedule, we reached 400 kV on the photocathode
gun without incident. Conditions at 350 kV are quiet, and we
therefore can now turn to the planned experiments. Today (25
Apr 97) we began making a photocathode, and we anticipate generating
electron beam early next week. The first planned experiments
involve commissioning the new multislit transverse-emittance diagnostic
that will ultimately be used to monitor the space-charge-dominated
10 MeV injector beam.
The laser was operated in support of diagnostics development and
operated normally. The new variable-speed electro-optic modulator
(EOM) was tested and found not to thermally bloom. It is installed
and synchronized with the existing EOM to support upcoming ITS
experiments. A new camera for monitoring the beam profile in
the clean room (and displaying it in both the clean room and control
room) was installed. In addition, the optical-transport system
was realigned. So, the drive-laser system appears ready for the
experiments.
The notable setback is that the ceramic warm window on the cryounit
cracked. This failure is similar in physical appearance to previous
failures that have occurred on test fixtures during qualification.
Initial indications are that the cause of this failure was running
high power rf (2 kW) through the window without adequate vacuum
in the vacuum waveguide. This is the same failure mode identified
in the previous tests, such as those done in the ring resonator
test assembly. The fundamental cause is attributed to running
rf in the ITS cave without functioning rf interlocks on the cavity
waveguide. The waveguide region is normally protected by three
interlocks, vacuum, arc, and IR. During this test cycle the vacuum
and arc interlocks were thought to be functional but were not
due to a wiring error that crossed readings from the two cryounit
waveguides. Steps will be taken to ensure this does not happen
again. Just prior to the failure the IR interlock had been disabled
with the belief that it was not functioning correctly, and this
likewise will not happen again. Rework and verification of interlocks
in the ITS cave and FEL Facility will be a high-priority item
prior to any cryomodule rf operations.
Although cryounit commissioning to date has provided a substantial
amount of useful data, the tests cannot be regarded as complete
because, due to the wiring error, there is no data on the waveguide
vacuum during high-power rf operations, and this data is key.
In view of this development, our current plans are as follows:
now- 5/2/97: Complete assemblies of two warm windows (currently in progress).
4/28/97-5/5/97: Qualify these windows using the resonant ring with the same procedures previously used.
5/1-12/97: Qualify these windows using the vacuum manifold with the same procedures previously used. Rework and verify ITS cavity rf interlock.
5/13-15/97: Install two warm windows, one if only one is available, on the cryounit in the ITS and cool down.
5/16/97: Verify interlock systems.
5/19-23/97: Complete cryounit cold testing.
5/26-30/97: Test rf systems and magnetostrictive tuners
FLASH -- Warm-window status as of 0930 today (25 Apr 97): electron-beam welding of two windows is slated to be finished today, at which time two fully completed warm-window assemblies will be ready for testing in the ring-resonator test assembly.
Accelerator Systems
Regarding the beam-transport system:
Fabrication of all dipole magnets continued unabated. The first-article
core for the optical- chicane dipole is nearing completion at
Everson Electric. They are able to achieve surprising uniformity
and linearity in the brass and mu-metal sheets, at the level of
a few ten-thousandths of an inch. This will allow matching thick
to thin tapers in a way that may eliminate major causes of field
nonuniformities. Success will only be testable at the Lab's Magnet
Test Stand, however. Since Everson is interested in full magnet
assembly, a draft assembly specification was generated and sent
for their comment.
A final detail of assembly was resolved by Northrop Grumman.
The problem is that as glue thickness approaches zero, shear stresses
in the epoxy at the edges of the mu metal and brass can grow to
very high values during temperature excursions due to differences
in coefficients of thermal expansion. Analysis indicates that
these stresses can be brought down to a third of the epoxy yield
strength with a simple chamfer or rounding to the edges of the
brass. The Engineering Change Order was sent to Everson for inclusion
in the manufacture of the brass pieces. The prototype dipole
will be glued today with this improvement, and preparations are
underway for including it in the remaining dipoles.
Magnet Enterprises International continued to wind and pot units
of the 16 coils for the optical- chicane dipoles, as well as design
and start fabrication of tooling for the coils of the reverse-bend
and injection/extraction dipoles.
Process Equipment Co. started burning steel to create the blanks
for the cores of the 180-degree dipoles and the reverse-bend dipoles.
Master Machine is starting to fabricate the cores of the injection/extraction
dipoles.
We made one more attempt to use the rectangular Panofsky trim
quadrupole. The main problem is that we have been unable to ascertain
its field properties with sufficient accuracy. We now believe
that by measuring only the dipole component at accurately determined
positions across the width we can assess its field quality. Starting
Monday, 28 Apr 97, we will attempt these measurements while bucking
out the quadrupole component with an existing QJ quadrupole that
is superposed and centered on the probe. In parallel, our lattice
designer will recast his specification in terms of this set of
measurements. The backup plan is to use a scaled-up QJ.
The drawings of the sextupole magnet coils were signed and sent
out for bid while the drawings of the core are being prepared.
Regarding corrector magnets (the need for which is discussed in
the "Commissioning/Operations" section below), examples
of cosine-theta distribution designs are being sought commercially
from television yoke manufacturers. We are obtaining papers that
document a simple design with good cut-off. Such a magnet was
built at Lawrence Livermore Lab in 1982 for fusion work. The
mu- metal design is being prototyped.
The written procedure to weld the X-chamber that will connect
the injection line to the recirculation loop is ready, and a flat
welding table was purchased to be delivered next Wednesday, 30
Apr 97. Girder parts for the back leg were delivered while all
22 QG quadrupole magnets passed their qualification tests on the
Magnetic Test Stand.
Multipole measurements on the ten QB quadrupoles surplused from
CEBAF were completed, and they passed their qualification tests.
The drawings for the optical-chicane vacuum chambers are almost
ready for signature. The design of the reverse-bend vacuum chambers
continued at Northrop Grumman, and one of their design engineers
visited Jefferson Lab for a day to go over details.
It had been thought that three quadrupoles of 4-inch aperture
were available for the recirculation- dump line, but this is now
uncertain. Were we to use existing QJ quadrupoles, higher-current
trim cards would be required, and we are in process of testing
this option. If unsuccessful, we will have to stretch the QJ
design into a quad with the desired strength. Procurement of
four additional QJs is in process, and if necessary, the order
would have to be changed to a stretched design on the fly.
Regarding cryomodule fabrication:
Progress on the cryomodule continued unabated this week. Leak
check of the first cryounit for the cryomodule was completed.
The second cavity pair completed retesting in the Vertical Test
Assembly, and the results are being analyzed. The third cavity
pair successfully went through final leak check; it therefore
passed acceptance tests and is being prepared for handover to
the cryounit-assembly crew.
Regarding electron-beam instrumentation and controls (I&C):
The balance of the cameras for the beam viewers and for the synchrotron
light monitors have been ordered.
Six beam-position monitors will arrive Monday, 28 Apr 97. We
will then certify they meet specifications and pass them on for
assembly into the back-leg girders. The remaining 19 will be
delivered by the following Monday, 5 May 97.
Half of the boards for the Machine Protection System have arrived
from Argonne National Laboratory. The rest should be here in
a week and need to be assembled.
The 400 boards for the ion-pump power supplies arrived; 200 of
these will be sent out for assembly; 80 for the IRFEL and 120
for CEBAF. The documentation for the vacuum-system crate design
is complete, and fabrication is starting. The racks are continuing
to be assembled in the FEL Facility.
A great deal of progress was made putting I&C-related information
on www, especially under section 5.11.2 of the Lab's FEL Documentation
Page.
Regarding rf systems:
A decision was reached concerning the design and installation
of the drive line for the master oscillator in the FEL Facility.
This will proceed in three phases:
(1) Install a 2-leg star system leading to the injector and the
cryomodule, and tie the drive lines to the low-contamination water
(LCW) line for temperature stabilization. In addition, install
10 MHz and 70 Mhz 1/4" distribution lines. Attempt to characterize
the LDF50-2 Heliax line to determine its phase-versus-temperature
set point. Perform microphonics measurements on the LDF50-2 line
to the injector to ascertain the line's temperature stability
in the presence of the LCW. (2) Install a 4-leg star, with drive
lines anchored to LCW, and measure the phase and temperature stability
of this system. (3) If necessary, incorporate active temperature
regulation.
FEL Systems
Wiggler
All drawings for the vacuum chamber and its support were checked.
A few minor changes were made by Northrop Grumman. We are now
in the process of converting the drawings to Jefferson Lab format
before going out for bid.
Final shimming of the wiggler center section is complete. The
ends should be shimmed by week's end. The rms phase error at
the design field of 2.8 kG rms is only 1.3 degrees compared with
the 5 degree specification. The peak-to-peak wander and angular
errors for that field are 19 microns and 680 microradians, respectively.
The calculated gain of the wiggler is within 2% of that of an
ideal wiggler of 40.5 periods. The calculated gain at the third
harmonic is within 2% of that of an ideal wiggler of 39.5 periods.
The width of the fundamental curve is the same as for a 40.5-
period ideal wiggler, and the widths of the harmonic curves are
the same as for a 39.5-period ideal wiggler. Certification scans
will be done next week, after which the wiggler can be shipped.
Optics
The custom 5-way crosses are now complete and ready for installation.
The custom-welded bellows were received and turned over to our
Machine Shop to have their flanges installed. The FEL I&C
Group built a motor chassis for the gimbal mount motors, and they
are operating smoothly. Another chassis is under construction
for the linear stages that will be used downstairs in the FEL
Facility. The layout of the optical-transport pipe is complete,
and we are beginning to order the hardware. Collimator development
continues to progress. The plumbing and electrical connections
to the carbon dioxide laser used for the mirror heat-sinking test
stand is installed. Testing should begin in two weeks, after
the safety interlocks and laser safety procedure are completed.
Commissioning/Operations
Considerable work has been done to specify and justify field requirements
for the corrector magnets. Standard CEBAF correctors have a 3%
error in the field uniformity. In the IRFEL, this could conceivably
translate into a factor-of-two error in downstream beam sizes,
whereas 1% field uniformity is probably acceptable. It will take
a considerable amount of time to generate accurate estimates by
way of simulations, and though these simulations will be started
shortly, we need to proceed with something sensible.
The three proposed methods for making magnets to meet the spec
are: 1) use a "cos-theta" design, 2) use a television
yoke magnet design, 3) add high permeability (mu-metal) material
in the magnet. While option (3) would work, there are places
along the machine without space to insert mu-metal magnets and
not have cross-talk between them and adjacent devices, an undesirable
circumstance. Consequently, we decided to avoid mu-metal magnets
where cross-coupling is a problem and use air-core correctors
with the best measured field uniformities in those locations.
Otherwise we will use option (3). If we can do no better than
3% with the best air cores we can get now, then we may look at
a retrofit after we have a better handle on the problem.
Facility
Work continued at a rapid pace this week in the upper level.
All lights are now powered as are all outlets in the lower level.
The drywall effort proceeded quickly with the north interior
wall covered, taped and sealed, as was the complete gallery hall
wall. Painting is scheduled early next week. The optical control
room and laser control room were sealed and painted. The first
two user labs were drywalled on all sides. In the areas with
complete drywall all electrical and signal conduits and outlets
have been installed. In much of the rest of the labs the conduit
and outlets are in position awaiting the drywall. The first electrical
step-down transformer for rf power is to be hung today (25 Apr
97). The main HVAC unit was hung in its final position. Windows
were put on the break room. Preparations for the windows in the
main gallery are almost complete. The bathroom areas were framed,
and plumbing is being installed. Most lab doors are now hung.
Pieces of the elevator have begun to arrive although no assembly
work has begun. The first set of waveguides were placed in the
respective penetrations. No fitting problems arose. A final
decision was made on placement of the low-contamination water
(LCW) lines in the rf gallery (along the north wall). We also
decided to anchor the drive line for the master oscillator to
the LCW lines. A set of drawings for that as well as services
to the laser labs will be signed next week. Lab services will
include rough vacuum, chilled water, LCW, dry nitrogen, and instrument
air. Interference with a house water line and a crane in the
injector pit was resolved by deciding to remove the water line
and supplying that route from upstairs.
Delivery of the tank for the high-voltage power supply (HVPS)
was delayed until next week; due to bad weather it could not be
painted. There was an issue about where to locate the HVPS tank
upon receiving it. Once installed into position in the injector
pit, it would impede installation of the photocathode gun. We
decided to place it out of position in the injector pit until
the gun is installed. This allows us to proceed with setting
up the HVPS tank despite its initially being "off-line".
The girder designs were completed for the two girders after the cryounit. We decided that the gas-handling system from the ITS could be used with only minor changes.