MEMORANDUM
To: J. Albertine, D. Helms, W. Skinner
cc: Division (M7), FEL Coordination Group
From: F. Dylla
Subject: IRFEL Weekly Report Sept. 30-Oct. 4, 1996
Date: October 4, 1996
Management
The Omnibus FY97 Spending Bill was signed by President Clinton
on Monday, 30 September. It includes $6M for continuation of
the Navy's FEL Program.
On Oct. 3 John Albertine and Fred Dylla gave a briefing to Eli
Zimet of ONR on the status of the Navy FEL program and discussed
possible outyear (97-98) activities with the FY97 funding increment.
We are actively coordinating our schedule for installation activities
in the FEL Facility with those of the Nuclear Physics Program
to ensure availability of the requisite manpower.
Progress on the construction of the FEL Facility has been rapid,
1-2 weeks ahead of schedule. In effect, this is motivating rapid
progress on machine design/procurements/fabrication to keep pace.
This circumstance accentuates the need for management to assure
product quality, and this need is receiving appropriate emphasis.
Injector Test Stand
We have been pushing toward routine operations of the gun in the
ITS. A meeting of ITS principals was held to identify impediments
to routine operation as well as to discuss plans to overcome them.
The immediate need is for written set-up procedures that can
be implemented by a nonspecialist. Deadline for this was set
for 8 October.
Injector commissioning was productive this week, progressing to
the point that we expect to start taking transverse-emittance
data next week. Activities included the following:
1) The photocathode continued to sustain a QE of about 2% without
resection.
2) We developed a procedure to center the laser on the cathode
using the remote mirror control motors in conjunction with monitoring
the electron beam as a diagnostic.
3) We measured the spot size on the cathode for use in the transverse
emittance experiments.
4) We solved the noise problem in the harp position readbacks.
5) We operated the injector at >1 mA average current with
a charge per bunch of 40 pC, commensurate with what is needed
for first light.
6) We operated the electro-optical modulators in the mode needed
for the transverse emittance tests, achieving the desired extinction
ratio of about 100,000:1.
7) We aligned the drive-laser optical path and connected the
remote laser monitoring head on the beamline.
Regarding development of the new HV stack:
1) Contrary to our plans, two metallized ceramics were shipped
overland to us last Friday, so we could not personally pick them
up and take them to the brazer (Hitemp, in California). Consequently,
this delayed the start of Kovar ring brazing. However, the parallel
work of getting the Kovar rings annealed and plated was started
by shipping the rings to Hitemp. We will use receipt of the ceramics
at Jefferson Lab as an opportunity to inspect them here and forego
an on-site vendor inspection. Thus, we now plan to go to Hitemp
in two weeks, at the end of the brazing cycle, and while there,
we will install the rotisserie for ion implantation at Lawrence
Berkeley Lab and start the implantation.
2) Tests of the ion-implanted samples with high dose rates yielded
good initial results. We started testing for survivability from
a 250C bake.
3) The electrodes for testing the coating for the cathode support
tube were cleaned and sent to FM Technologies for coating.
4) Polishing of the new cathode support tube is on time, reaching
15 micron diamond grit, and machining of the Mid-Voltage Ring
is nearly finished, per schedule.
The cryounit is fabricated and installed in the SRF Test Cave.
It is presently at LHe temperature and is vacuum tight. Acceptance
testing starts in earnest on Monday, 7 October.
We made progress toward obtaining hardware required to reconfigure
the gun's beamline for parallel measurement of the beam's transverse
and longitudinal emittance. This includes ordering optical modulators
for the drive laser that will increase the ghost-pulse extinction
ratio for better sensitivity in the longitudinal-emittance measurement.
It also includes completion of the coil for the necessary focusing
solenoid, and fabrication of the magnet's core was started at
an outside vendor.
Accelerator Systems
There has been considerable and on-going interaction between the
beam-transport designer and the magnet engineers toward resolving
how best to deal with the fringe fields of the dipole magnets.
The present strategy continues to be to use a saddle-coil configuration
with field clamps that localize the fringe fields. Preliminary
beam-transport analysis indicates that, with this design strategy,
the impact on the machine design will be extremely small, perhaps
a 2-3 inch displacement of the 180-degree bends. We anticipate
timely resolution of this matter.
A detailed set of particle-tracking studies indicates, even under
overly pessimistic circumstances, no need for an electron-beam
scraper between the cryomodule and the wiggler. Indications are
that a scraper placed in the first high-dispersion region of the
first recirculation bend will add insurance for low (100-nA-level)
beam loss during energy recovery. Additional analysis is slated
to quantify this notion.
Held internal review of the multislit diagnostic project. The
prognosis is looking good for automated transverse-emittance measurements
of the space-charge-dominated 10 MeV beam with one-second updates
and with accuracy approaching 10%. The project is on track.
Testing of the beam-position monitors (BPMs) has begun to establish
their utility for the IRFEL. The "BPM test stand" is
essentially an analog computer, a suite of electronics that replicates
the signal that a BPM would see as the electron beam sweeps by
it, and it is used to measure the response of the BPM's electronics.
This methodology has been benchmarked with the nuclear-physics
machine, where it is found to be very accurate, and the methodology
was easily modified for application to the IRFEL. Initial tests
of the 4-channel BPM electronics for the IRFEL are favorable,
as had been anticipated.
A procurement package for the electronics racks and doors needed
for the IRFEL was prepared, signed off, and forwarded to our Procurement
Office.
FEL Systems
Wiggler
Corrected assembly drawings were received from the vendor and
the procurement of components for the wiggler appears to be on
track. Using the top level drawings we are now able to initiated
design of the vacuum pipe, mounting system, beamline insertable
viewers, and support table. That work began this week with conceptualization
of the support approach for the beamline. The planned design
allows us to use an optical bench girder with no holes which is
very cost effective. Work is proceeding on schedule.
Optics
Following the successful review of the resonator system last week,
procurement of the resonator components was begun. Orders for
the vacuum components, mounts, and stages were initiated. Detailed
drawings for fabrication are in check. From earlier diagnostic
orders a low level 2 micron camera for viewing the synchrotron
light was received. Also received was a highly quantum efficient
thermoelectrically cooled line camera with response to 1.8 microns
which will be used to align the electron beam in the wiggler.
The initial set of components were ordered to perform a thermal
distortion measurement of cavity mirrors in their mounts on the
bench.
Operations/Commissioning
Tracking analysis to determine need for scrapers was completed,
and the requirement has been inserted into the "engineering
queue". The vacuum-pipe apertures were verified to be large
enough that beam loss is not expected to be a serious problem.
Nevertheless, we plan to add a single scraper with adjustable
aperture in the first high-dispersion region of the first recirculation
bend. Its purpose is two-fold. First, it will suppress beam
loss in the presence of unusually high energy spread, as might
be generated in experiments involving high-efficiency extraction
from the wiggler. Second, it can be used in experiments to study
the interplay between beam loss and rf stability. Aside from
these benefits, it will provide insurance against uncertainties
in the distribution function of the beam at the wiggler exit.
Engineering this scraper is nearly identical to engineering the
insertable dumps.
Facility
Facility progress continues ahead of schedule. The sixth of seven
wall pours was completed this week for the lower level and work
continued on framing the ceiling pour. The first of three pours
of the three foot thick concrete ceiling slab will commence tomorrow
with the west end of the building. The second pour is scheduled
for the following Wednesday. The final wall pour is also expected
so that the entire lower level will be surrounded. The contractor
was awarded the third safety incentive payment in August for having
no safety citations during that period. (There were also none
in September and the contractor will receive an award for that,
too, next month.). Several scheduling issues regarding joint
occupancy in January were discussed at the monthly contractor
meeting and several approaches were identified which may simplify
the initial installation tasks by TJNAF personnel.
A meeting was held with Mike Kelley (DuPont) on Oct. 4 to continue
discussions of the fit-up of the polymer processing laboratory.