MEMORANDUM
To: J. Albertine, D. Helms, W. Skinner
cc: Division (M7), FEL Coordination Group
From: F. Dylla
Subject: IRFEL Weekly Report, March 10-March 14, 1997
Date: March 14, 1997
Management
A revised proposal and statement of work for the 1 µm IR
FEL upgrade was sent to the Navy High Laser Office that incorporates
their preliminary comments on the first draft.
The second meeting of SURA's Maritime Technical Advisory Committee
has been scheduled for June 11-12.
Management focus this week was on coordination of the near term
ITS schedule, progress with the rf windows, and start-up of installation
activities in the first floor of the FEL building.
Injector Test Stand
We continued operating the photocathode gun at 250 kV. We calibrated
the viewers for the multislit transverse-emittance diagnostic
which will be commissioned with the upgraded gun. In the process,
we also generated a test set of multislit data using the existing
slit assembly to provide example data for analysis. A measurement
of bunch length versus transverse position on the bunch was made
using the rf kicker cavity. Measurements like this provide information
on the three-dimensional density profile of the bunch for comparison
with code. We also did a continuous-wave run to test photocathode
life, and in the process delivered 10 coulombs to the beam dump.
This run was controlled and monitored from the Machine Control
Center on the accelerator site.
The infrared-wavelength optical modulator and the bias supply
for one of the two 527 nm optical modulators failed during this
week's runs.
Regarding upgrading the photocathode gun:
In attempting to assemble the new high-voltage stack, we detected
an error in the position of the kovar flanges on the new ion-implanted
ceramics. The rings were brazed in a position 0.5- 2 mm higher
than specified. Thus, we spent the week working a solution to
bend the flanges to close the resulting gap using tooling that
will not stress the delicate braze joints. At week's end that
tooling is scheduled for completion on Saturday. As a back-up,
we made a second tool to do bending by hand. We might use the
back-up ceramic to replace the most severely misbrazed ceramic.
It was ion-implanted at Lawrence Berkeley Lab to a resistance
centered within the range of the two ceramics we have on hand,
and we will receive it from LBL on Monday. The bottom line is
that we plan to weld the high-voltage stack not later than Tuesday,
18 Mar 97. We plan to continue operating the gun in the ITS until
we have completed fabricating and leak-checking the new stack,
which, again, should be early next week.
The coated cathode-support tube was electron-beam welded to its
flange and cleaned in preparation for installation. We decided
to remove the spacer from the photocathode gun when upgrading
it for higher- voltage performance. At 350 kV voltage, this action
will result in a direct-current field gradient of about 7 MV/m
at the cathode, as opposed to 4.2 MV/m with the spacer in place,
and is therefore favorable from the perspective of electron-beam
dynamics. The action is regarded to be low-risk because the highest
fields on the cathode support tube and ball are near the equator
of the ball and are insensitive to this change-out.
Regarding other ITS activities:
Qualification of ceramic warm windows continues. We have found
that the supplier has not been producing ceramics of consistent
quality. We successfully ran two warm windows to 25 kW with the
50 kW klystron setup, and thus, as of now, we have two windows
for the cryounit and plan to install them early next week for
subsequent off-line cryounit tests. Contingency plans are being
developed in the event there are problems. Control software for
the cryounit is in final debugging.
Due to problems with a vacuum leak, the spare 50 kW klystron (the
fourth unit) was removed from its test stand and is being returned
to the vendor for repairs. We are anticipating a turn-around
time of about two months.
Accelerator Systems
Regarding the beam-transport system:
The bids for the optical-chicane dipole magnets were received.
One vendor requested an extension to close-of-business Tuesday,
March 28. Since this bid is the first in the series of three
bids for dipoles, we did extend the due date to keep this qualified
vendor in the running and enhance our ability to maintain parallel
manufacturing of these magnets.
The second dipole-magnet bid package (for the reverse-bend and
180-degree dipoles) is one-third complete, missing our intent
to get all the drawings out for bid by Friday. The prints for
the 180- degree dipole are lagging the furthest behind. Were
we not to intervene, they would arrive next Thursday. However,
we are attempting to accelerate sign-off. The package's check
prints were checked during the week and sent back to Northrop
Grumman on Friday. We are taking a portion of the Northrop Grumman
electronic files and working in parallel to incorporate these
back-check items. As good news, the completed drawing package
for the first reverse-bend (DX) dipole was received on Friday,
and the package for the second reverse-bend (DQ) dipole is due
to arrive from Northrop Grumman on Monday.
Design of the injection-chicane dipoles continued at Jefferson
Lab, also missing the target Thursday date for getting them out
to bid. Check prints are in evaluation and the package is being
worked over the weekend.
We are working to create an industrial process to make the Purcell
gap and glue the mu-metal onto the poles of the dipole magnets.
Tests that involved gluing aluminum shim material between two
1-ft-square aluminum tooling plates under very uniform, high-pressure
conditions showed that virtually zero epoxy thickness was obtainable.
We will therefore try again with the prototype dipole using similar
bonding methods. We plan to evaluate the shear stress on this
epoxy bond at Northrop Grumman. Tests of other methods for creating
the Purcell gap are also planned.
Tests with the prototype dipole with welded vacuum chambers indicated
slight alteration of the edge of the good-field region in three
locations. Two of those locations were rectified by increasing
the width of the as yet undetailed chambers. The third location
is at the intersection of the injection line with the recirculated
beam line. It has no solution, but from the perspective of electron-beam
dynamics, we can live with the small effect.
Design of the vacuum chambers for the optical-chicane dipoles
began. We also started establishing the cleaning procedures and
equipment to fabricate all of the vacuum chambers under the particulate-free,
ultra-high-vacuum conditions required by our specifications.
Eight weak quads were shipped from the vendor. All are beautifully
made but failed inspection due to an irregularity in the length
of one of their poles. We are working that issue.
The magnetic optics of the recirculation-dump line was finalized
and incorporated into the master layout. We need two additional
wide-aperture (4-inch) quadrupole magnets for this line, much
like our QTS. They will have to be added to the procurements.
The back-leg stands and cable trays were installed in position,
marking the first part of installation of the beam-transport system
in the FEL Facility.
Drawings of the remaining stands and girders for first light were
signed off, and their procurements were started.
Regarding cryomodule fabrication:
Cryomodule assembly has begun. Following successful acceptance
tests of the first cavity pair, assembly of the first cryounit
is now started. The second cavity pair has been assembled and
is scheduled for acceptance testing next week.
Regarding electron-beam instrumentation and controls:
The balance of the drawings for the Oregon Micro Systems (OMS)-based
stepper-motor-control system were completed and signed off. All
of the constituent boards are complete or in fabrication.
Design of the vacuum-control crates continues. They will hold
67 individual printed circuit boards of 9 different types. Only
the fast valve control card has not yet been manufactured.
All of the hardware necessary for mounting and testing the multislit
transverse-emittance diagnostic with the upgraded photocathode
gun is now ready.
The optics setup for detecting synchrotron light in the vacuum
chambers of the 180-degree dipole magnets was successfully bench
tested using the same optics and geometry to be installed in the
linac arcs. The system will permit non-invasive imaging of the
beam at a point in the transport dominated by dispersion. This
enables sensitive energy stability and energy spread determinations
of the electron beam to be made. The camera to be used has also
been tested and is expected to have sufficient sensitivity to
even see pulsed beam while setting up the beam transport.
FEL Systems
Wiggler
Gage blocks for supporting a 12 mm wiggler gap were ordered from
STI Optronics. Delivery of the magnets from Shin Etsu has slipped
again and is now projected for 24 March, with expected delivery
of the wiggler in late April. The design layout for the wiggler
vacuum-chamber stand is nearly complete. We will make the tubing
necessary for the chamber in house. Techniques from other labs
that have made similar tubes have been gathered.
Optics
Efforts on the new design for the optical collimator have been
somewhat slowed by the unexpected resignation of the designer.
We are in the process of hiring new designers, but this may delay
our efforts by several weeks.
Our machine shop reports the output Brewster window is about 50%
complete. This will complete the work they can do until several
long-lead items are received later this month or early next month.
We ordered mirrors for 5-micron operation. We also ordered hardware
to support installation of the optical-transport system in the
FEL Facility.
Operations/Commissioning
A procedure for setting up the electron beam prior to wiggler
installation was drafted. Part of the consideration is doing
early experiments concerning the effects of coherent synchrotron
radiation on the electron beam. The quad-viewer method for making
transverse-emittance measurements in the back leg of the recirculation
arc was detailed, and correspondingly the precise locations of
the optical-transition-radiation viewers were pinpointed. Generally
speaking, we are in process of freezing the precise locations
of all of the elements of the beam-transport system, which must
be done in time to implement the installation plans. So far,
all of this activity is on track.
Facility
FEL Facility construction and installation proceeded at a rapid
pace. The most visible progress is upstairs where wall frames
and studs were placed around the entire lobby area and entire
utility room. About half of the roof decking is in place. Some
door frames are in place. A striking view now exists from the
east side with all exterior wall panels attached. Large quantities
of HVAC equipment and ducting were craned to the second floor.
Plumbing work continued on the bathrooms. It is starting to
look like a laser facility!
No less important was lots of detail work performed downstairs
including finishing the floor sealing and painting the ceiling
and piping. Doors were hung on all exits and painted. The exterior
roll-up door to the truck ramp was hung and is fully operational.
Work continued on the site electrical service. It may be possible
to power up the main lighting for the lower floor next week.
Survey crews marked the placement of the cryogenic lines and the
lines were wrestled into position. A welding trailer was moved
into the area as welders set up to begin connecting the pipes.
Markers for the optical transfer lines were surveyed on the ceiling
setting the stage for hanging of the transport piping next week.
All back-leg stands were bolted to the floor becoming the first
set of transport elements to be installed as planned. Jefferson
Lab personnel continued the installation-planning efforts to the
second floor area (first floor task list is in good shape and
we are proceeding according to plan). Additional personnel were
assigned to detail the electrical rack installation, hookup and
site power coordination. A draft of the initial wiggler installation
and alignment was produced and reviewed.
Fabrication of the high voltage tank proceeds on schedule. Design started for the crane rails and clean hood in the injector area. A site review for the clean room is tentatively scheduled for 25 Apr 97.