MEMORANDUM
To: J. Albertine, D. Helms, W. Skinner
cc: Division (M7), FEL Coordination Group
From: F. Dylla
Subject: IRFEL Weekly Report, February 24-28, 1997
Date: February 28, 1997
Management
The DOE Basic Energy Sciences Program Office held a review of
the IR Demo project and the Jefferson Lab FEL program on Feb.
23-25. The review was co-chaired by the Navy (John Albertine)
and included six external reviewers. The review team gave the
project excellent marks for the execution of the Demo project
to date. A draft report is expected from the Team next week.
Dylla and Helms have been invited to DOE-BES headquarters on
March 6th to discuss continued interactions with BES.
A special effort was made this week to expedite the procurement
efforts of the electron beam transport hardware (primarily the
magnets), in order to eliminate the present negative schedule
variance on this task and to ensure timely delivery of this hardware
for the installation tasks.
Detailed scheduling efforts continued on two fronts: a new schedule
for the Injector test Stand, reflecting the decision made last
week to concentrate ITS efforts on gun testing and RF testing
of the quarter cryounit.
The January monthly report was completed and distributed on Feb.
28th
Summaries of the Demo project and the December MTAC report were
prepared for delivery to the Virginia Congressional delegation
per their request.
Injector Test Stand
We started 24-hour operation of the photocathode gun at 250 keV,
running three full days this week. In conjunction with gun operations,
we aligned the drive laser to the photocathode, hard aperture,
and camera in the test cell to permit laser-beam analysis. In
general, the drive laser was brought back to a fully operational
state. We also recesiated the cathode and brought it back up
to several percent quantum efficiency. Subsequently, we made
about 20 measurements of transverse emittance to verify the performance
of the new hardware in the beamline and the reproducibility of
measurements taken last November, and to quantify the effect of
the rf kicker cavity on the beam. No effects have been observed
which are directly attributable to the kicker cavity. However,
we did have a failure of the kicker's high-power amplifier. After
replacing it, we continued commissioning the rf system. In particular,
we operated the kicker cavity in both cw and pulsed modes, achieving
to date about 100 W cw and peak powers in the pulsed mode up to
about 250 W. This performance is already adequate for the planned
longitudinal phase-space measurements, but we are in the process
of boosting the kicker cavity's performance to provide additional
capability.
Regarding upgrading the photocathode gun:
* Coated Cathode-Support Tube - Electron-beam welding of the
newly coated cathode support tube is being preceded by a weld
test, scheduled for the middle of next week, on the sample tube
that FM Technologies used to calibrate the coating machine. The
test will tell us if there are any variables to watch for while
welding and cleaning the cathode support tube.
* Ion-Implanted Ceramics - Lawrence Berkeley Laboratory achieved
a bulk resistance of 2.8x10^9 ohms on the second ceramic, very
near the target value of 2.5x10^9 ohms. They started implanting
the first ceramic (after its original over-shot implantation was
removed) using the continuous resistance-monitoring system they
developed. LBL plans to ship a matched pair of ceramics today.
One back-up ceramic will have its flanges brazed on at Hitemp
and be sent to LBL next week for its implantation. The remaining
three oxide-coated ceramics are at Hitemp, awaiting full success
with the ion-implantation technique before having their coatings
removed.
Regarding other ITS activities:
There has been considerable activity toward qualifying warm windows
for the injector cryounit. The resonant ring test facility was
run with a single warm window and with no vacuum in the system.
The window was exposed to rf power up to 50 kW with no breakage.
A second window is now being tested. Additionally, the vacuum
test fixture was reworked. It should be under vacuum and ready
for tests by Monday, 3 March. Qualification of the 50 kW rf system
for window testing is also scheduled for Monday.
Acceptance tests of the spare 50 kW klystron are continuing.
In addition, the software and screens for the cryounit were successfully
tested. The software for the mechanical tuners was also installed.
Accelerator Systems
Regarding the beam-transport system:
Design of the 180-degree dipole magnets started up again since
the back-check changes to the optical-chicane-dipole drawings
were completed at Northrop Grumman. The prints and specifications
for the optical-chicane dipoles were sent Thursday evening (27
Feb) via overnight mail to vendors for bid. The design of the
first reverse-bend dipole magnet was completed, and the drawings
of the second reverse-bend dipole was started.
Design of the injection-line dipoles continued at Jefferson Lab
with a projected completion date of March 14.
The prototype dipole magnet was used to test the effect of vacuum-chamber
welds on its magnetic field. We found that 304 stainless steel
provided good field uniformity across the whole chamber, better
than 316 stainless steel. Accordingly, we have decided to use
304 stainless steel for the vacuum chambers. We also learned
that we will need to test each chamber by running it in a magnet
while using a field probe to measure the additional field contributed.
We plan to use this contribution in combination with the natural
variation among the family to mix and match the dipoles, making
it easier to meet specifications for the absolute field value
versus current. If this does not work, then we will have to shim
the back legs among a family. This later option will add a significant
amount of time to magnet measurements.
The prints for the differential pump station were signed. Design
of the back-leg girder was put on hold to integrate vacuum pumps
into all girders, and the injection-dipole girder is undergoing
a last check by the alignment group. Most of the stands supporting
the first-light portion of the machine are now in an advanced
state of design and detailing, and sign-off of most of these items
will take place next week.
Design of the vacuum chambers in the remaining first light regions
started.
The request for bid on the two 100 A power supplies needed for
the injection and extraction chicanes was sent to the power supply
vendor.
The prototype trim quadrupole magnet underwent detailed magnetic
measurements, and we are in the process of analyzing the data.
The prototype sextupole magnet underwent preliminary magnetic
characterization. Its fringe field is high enough to merit adding
a field clamp to contain it. We presently do not have a probe
that can accurately characterize the multipoles on this 8-inch-bore
device. Therefore, we made plans to construct such a probe from
existing hardware and will use it to identify an optimal pole-tip
profile. In the meantime, we will proceed with final design and
procurement of sextupoles with square-edged pole tips and with
provisions for field clamps. The pole tips will be removable,
allowing us to customize their shapes at a later date.
Regarding cryomodule fabrication:
A delivery of twelve higher-order-mode (HOM) flange assemblies
was returned to the vendor because they did not comply with drawing
specifications. We do not anticipate this affecting production
schedule.
The first cryomodule cavity pair finished testing this week in
the Vertical Test Assembly. Preliminary analysis of the data
is positive. Gradients are 10 MV/m or higher with little or no
field emission evident. The second cryomodule cavity pair is
scheduled for assembly on Tuesday (4 March).
Overall, cryomodule production proceeded nicely this week. In
addition the warm-window testing results described above under
"Injector Test Stand" support the idea that artificially
high vacuum conditions during testing was the cause of limited
window performance.
Regarding electron-beam diagnostics:
A preliminary investigation was made regarding the possibility
of testing the multislit transverse- emittance diagnostic at 350
keV and low current, nominally 10 pC per bunch. Simulations
indicate that the resulting emittance is in the measurable range
of the device. Accordingly, we have begun making plans to install
the device on the experimental beamline in conjunction with upgrading
the gun in the ITS, and then test it during the last part of April.
As anticipated, we received the shipment of 13 beam viewers.
FEL Systems
Wiggler
Wiggler development continued on schedule.
Optics
Efforts proceeded toward a new design for the optical collimator.
Fabrication of optical-cavity components included the camera
mounts and the output Brewster window. Installation drawings
for the optical-transport pipe on the ground floor are being modified
to use the same coordinate system as the rest of the machine.
The drawings for the near-Brewster-window assembly are complete
and ready for signature.
The Aerotech linear stage for controlling the optical-cavity length
was received this week.
Operations/Commissioning
Plans were documented for experiments to measure transverse-emittance
growth from coherent synchrotron radiation (CSR) in the bunch
decompressor following the wiggler location, and in the first
recirculation arc. As currently envisioned, the emittance measurements
will involve quadrupole magnets and viewers at the wiggler location
(with the wiggler removed), downstream of the bunch decompressor,
and in the back leg (which has a multiplicity of measurement systems).
Parametric investigations of the influence of bunch charge, bunch
length, bunch momentum spread, transverse bunch size, and transverse
emittance at entry to the bending systems are all envisioned.
We anticipate being able to start taking CSR-related data around
the turn of the calendar year.
A decision was made to retain the scraper in the first recirculation
arc. It will localize the potential loss of particles with large
energy offsets, as might be produced as a result of the lasing
process in the wiggler. Likewise, it provides a nice diagnostic
of the wings of the longitudinal phase space emanating from the
wiggler, making it a valuable tool for FEL experiments. Specifications
were established that permit the scraper to serve as an excellent
energy-distribution and halo diagnostic, as well as in its nominal
machine-protection role.
A series of sensitivity studies were done by way of numerical
simulations as part of developing detailed specifications for
the magnet measurements envisioned for the injection-line dipole
magnets. The basic plan is to procure these magnets, measure
them to now-specified accuracies, and then do follow-on computer
modelling that incorporates measurement results to optimize the
resultant electron-beam dynamics. There are no significant difficulties
anticipated with this approach.
Facility
Framing of the upper level continued with the result on Friday
(28 Feb) that the upper-level frame is complete in place. The
roof decking was placed in the lobby area, and wall frames were
started in two regions of the upper lobby. In the lower level,
the high power electrical pulls were underway, as was touch up
painting and cleanup in both the main room and the entrance labyrinth.
The set of completed cryogenic transport lines were transferred
to the Facility in preparation for the lengthy installation process.
Schedules were reviewed in a monthly meeting with the contractor.
The contractor admits to a 3-week schedule slip against the March
15 contractual BOD 2 (upper level). This was primarily caused
by problems with one of their subcontractor's miscalculations
on the framing. It now appears the upper level will not be fully
dried in until the third week of April. The contractor was sent
a "get-well" letter by Jefferson Laboratory contracts
personnel reminding them of the $1500/day penalty against BOD
2. The delays in BOD will affect the equipment installation schedule
upstairs, cause more work to occur in the summer, and press the
availability of installation personnel to keep the schedule on
track.