To: J. Albertine, D. Helms, W. Skinner
cc: Division (M7), FEL Coordination Group
From: F. Dylla
Subject: IRFEL Weekly Report Sept. 23-27, 1996
Date: September 27, 1996
On Sept. 24-26 we hosted a workshop on scaling FELs to the megawatt-power
class for Northrop Grumman and the Navy High Energy Laser Office.
Approximately 50 people attended the workshop which included
representation from all the major laboratories in the US with
FEL activities. Two classes of baseline machine concepts were
examined: (1) a regenerative amplifier and (2) an oscillator
with energy recovery. A list of high-level technical issues
were identified for working groups to examine the necessary technology
extrapolations and technical risks from existing demonstrations
to high-power devices of interest to the Navy. Workshop summaries
will be distributed to all attendees.
A successful review of the optical cavity design for the IRFEL
Demo was held on Sept. 26.
Injector Test Stand
Injector commissioning activities included the following:
1) High frequencies were found to be present on the harp-position
potentiometers. They are associated with the stepper-motor controls.
New hardware, combined with modification of the software driver,
is in development to eliminate current to the harp during the
2) The software to be used to take transverse emittance data
in an automated fashion was successfully tested.
3) The photocathode's quantum efficiency remained relatively
constant through the week at between 2.6 and 3.9%.
4) This week we ran beam up to 0.5 mA average current and 13 pC
per microbunch. We found that the beamline's ion pumps had problems
with ground currents, which were subsequently corrected.
Regarding development of the new HV stack:
1) Final processing of the ceramics for the new stack is finally
at hand, about a week behind schedule, with two promised to be
available Sept. 30. On Tuesday, 1 October, a representative from
Jefferson Lab is slated to pick up the two ceramics from the supplier
(WESCO) and take them to HiTemp for brazing. The kovar rings
are in machining, and HiTemp is scheduled to start brazing next
2) The final ion-implantation samples are being delivered, and
the ion-implantation rotisserie parts are undergoing small corrections.
3) Coating the electrodes to test the usability of the FM Technologies'
coating for the cathode support tube is about a week behind schedule.
4 Polishing of the new cathode support tube is on time, reaching
600 grit and machining of the Mid Voltage Ring is nearly finished,
Fabrication of the injector cryounit is essentially complete,
and the cryounit will be installed in the SRF Test Cave on Tuesday,
1 October, where it will undergo acceptance tests.
Testing of the prototype dipole magnet indicates that the field
clamps at the magnet apertures didn't suppress fringe fields to
within specified levels. Initial design of a saddle-coil configuration,
with field clamps that are expected to solve the matter, took
place this week. Formally, the dipole magnets are about one month
behind schedule, but they are not on the critical path, and this
schedule slip is not affecting the Sept. 97 milestone for hardware
installation in the FEL Facility.
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.
Designs of multislit apertures (for transverse emittance measurements
of the 10 MeV electron beam) and their mountings were completed,
as were the associated data-reduction algorithms. There are two
designs, one for an unshielded aperture for the 10 MeV dump line
to be used in running the injector after it is moved from the
ITS to the FEL Facility, and one shielded aperture for the acceleration
line preceding the cryomodule to be used in commissioning the
FEL. An internal design review is scheduled for next week. If
successful, the drawings will be detailed and the hardware will
go into fabrication.
A procurement package for all of the shielded beam viewers required
for the IRFEL was prepared, signed off, and forwarded to our Procurement
Final drawings from STI Optronics were delayed due to problems
at the vendor's CAD subcontractor. We now expect to receive corrected
copies of the final prints next week. This should allow us to
approve the mechanical design and start design work on the vacuum
chamber and support next week. There should be no impact on the
schedule since design approval has been given and parts are being
Following approval of the resonator hardware at the Optics Review
9/26 (see management section) procurement of components was initiated
with the purchase of optics blanks and vacuum components. A few
minor drawing changes were initiated based on suggestions by the
engineering review team which examined the drawings in parallel
with the scientific staff review. Drawing signoff is expected
next week to release components for fabrication. That will allow
the component performance tests planned to proceed on schedule
later this fall and early winter.
A list of all the current FEL beam diagnostics has been compiled
and posted on the WWW in Section 5-1-7 of Jefferson Lab's FEL
documentation. This list constitutes the baseline for the diagnostic
suite and determines the associated development plan.
It was incorrectly reported last week that part of the ceiling
had been poured. In fact the forms for the ceiling pour in the
west third of the building were established. Those forms were
extended this week to the western two thirds of the lower level.
In addition walls were extended in the second third, and the
pour for the lowest-level floor was completed. Wall forms have
been placed in much of the east end. The overall building schedule
is on track despite a very wet summer, and no significant problems
are currently noted in the design or parts constructed.
Concerning plans for injector reinstallation: Held first installation
planning meeting and identified a set of related action items.
These include identifying cables needed, reviewing the cable
tray layout, and identifying the options for moving or replacing
the laser clean room.