MEMORANDUM
To: J. Albertine, D. Helms, W. Skinner
cc: Division (M7), FEL Coordination Group
From: F. Dylla
Subject: IRFEL Weekly Report Jan. 20-24, 1997
Date: January 24, 1997
Management
We held the winter workshop of the LPC on January 21-22 and approximately
65 attendees were present. Fifty participants were from outside
the lab. Three of the working groups, polymer processing, metal
processing and micromachining made good progress towards planning
for initial utilization of FEL user laboratories. Plans for a
fourth laboratory presently designated for use by personnel from
the Navy and NASA are still in an early stage of discussion.
No firm commitments are in place from NASA yet nor could be represented
by NASA attendees at the workshop. Proposed experiments by the
NRL staff are projected to require only a small amount of beamtime.
There were preliminary discussions at the workshop on mechanisms
for laser user interaction with the user facility, methods of
allocating beamtime and draft user facility agreements.
The DOE distributed the preliminary agenda to the reviewers for
the February 23-24 review. During the LPC meeting, commitments
were obtained from three speakers for the FEL applications section
of the review.
Injector Test Stand
The cesiator on the gun was successfully recharged and the unbaked
GaAs wafer in the gun was tested with white light. A photocurrent
three orders of magnitude above background was achieved with a
42 volt bias. This is a positive result and indicates proper
operation of the cesiator and cathode.
Preparations continued toward baking the gun and beamline to allow
the new beamline configuration to be tested at lower voltages
(250-300 kV) with the current ceramic stack on the gun. By checking
systems, software and beam dynamics now, we will be able to optimize
our operating time at 350 kV once we upgrade the gun. The vacuum
bake of the beamline and gun started 23 Jan and will continue
until 27 Jan. We will then start reassembling the non-bakeable
portions of the beamline and gun, and plan to resume operating
the gun during the first week in February.
Regarding upgrading the photocathode gun:
* Coated Cathode-Support Tube - FM Technologies reports that
they will finish coating the cathode-support tube by the first
or second week of February.
* Ion-Implanted Ceramics - Lawrence Berkeley Lab (LBL) continued
to implant the "dummy" ceramic to a dose of 7.5x10^16
per square cm, and they obtained a resistance of 2.4x10^10 ohm,
right in the middle of our target range. Unlike the Cr/V-oxide-coating
process, the ion- implantation process offers far better control
of, and provides a real-time in-situ measurement of, the resistance.
The refurbished leak-test fixtures were received by Hitemp, and
the subsequent leak test of the braze on the flanges of the first
improved ceramic was successful. That tube was cleaned and sent
to Lawrence Berkeley Laboratory for implantation while they take
care of accumulated work, improve their electronics, and prepare
for the next runs. We are buying some 1/4" platinum rods.
They will be required to complete the second improved ceramic.
* Cr/V-Oxide-Coated Ceramics - In view of LBL's success, we plan
to remove the Cr/V-oxide coatings with the unacceptably high resistances
on the three other ceramics and substitute the ion- implanted
surface.
Accelerator Systems
Regarding the beam-transport system:
The close-out meeting of the Dipole Magnet Review was held on
22 Jan. The review committee concluded that we should proceed
with procurement of the optical-chicane dipoles. However, a number
of actions remain. Two are of note. The first action is the
need to confirm, via measurements on the prototype dipole, that
a suitably uniform drop-off of the end field required across the
"good-field" aperture can be obtained. The dipoles
are already designed to be wider by a half gap on each side to
provide the drop-off, but the increased width may not be enough.
The second action is to consider a method for orbit correction
that minimizes use of corrector dipoles, thereby simplifying machine
operation. The method is physically to shift the sextupoles and
trim quads in the recirculation arcs. The idea will be modeled
using our linear-optics code.
The design of all of the recirculation-bend dipoles continued
at Northrop-Grumman in parallel with checking the drawings of
the optical-chicane dipoles. Specifications were written for
manufacturing the optical-chicane dipoles, and their procurement
packages are being prepared.
The layout of the injection/extraction dipoles was solidified
based on measurements of the prototype dipole, including saddle
coils and field clamps. One net result is that the magnets are
larger in size. In the extraction region leading to the recirculation
dump, there are two phasing dipoles in close proximity to the
extraction dipole. Thus, the larger size of the extraction dipole
is of concern because its edge fields could be warped beyond specifications
by the presence of the constituent iron in the nearby phasing
dipoles. Based on favorable high-field performance of the prototype
dipole, we are presently considering a work-around that involves
increasing the maximum design field in the extraction dipole and
eliminating the phasing dipoles altogether.
Measurements of the prototype trim quadrupole and the prototype
sextupole have been delayed in favor of additional measurements
of the prototype dipole and of magnets supporting the main machine.
We cannot continue the delays indefinitely and are searching
for ways to expedite the measurements.
A kick-off meeting on the girder for the injection dipoles was
held to review the requirements document for these girders. Kick-off
meetings are now planned for the remaining stands that are needed
for the beam-transport system supporting first light. The X-chamber
drawings (for the vacuum chamber connecting the injection line
to the recirculation loop) are now in our machine shop.
Regarding cryomodule fabrication:
The pursuit of ceramic warm windows continues. Testing of the
warm-window assembly mentioned in last week's report was unsuccessful
because the ceramic cracked. We now conjecture that the problem
may not be with the window assemblies, but with the vacuum in
the ring-resonator test stand. Consideration of existing experimental
data revealed that the combination of the test-stand vacuum conditions
and the field gradient at the ceramic window is conducive to rf
breakdown. In response, we spent this week improving the vacuum
and are preparing another window assembly for testing. The improved
vacuum corresponds to that expected in an operating cryomodule,
so the improvements to the ring-resonator test stand serve to
make it a better model of the windows' operational environment.
We now have on-hand four stainless-steel higher-order-mode (HOM)
subassemblies. Two of them were tested and passed all of our
standard acceptance tests. As an additional check, we are in
process of qualifying them in a cold-cavity assembly.
Our machine shop has started to modify a standard CEBAF liquid-He-containing
vessel to incorporate penetrations for the FEL HOM designs. This
activity is on schedule.
Regarding electron-beam diagnostics:
As the prototype stripline beam-position monitor (BPM) was being
modified to incorporate shorter electrodes, three of the four
electrodes shorted to the end ring during the final weld. This
is being corrected. Acceptance tests require two adjacent electrodes
to function.
A memo documenting the results and decisions of the BPM Review
has been drafted and is circulating among the Review Committee
members for comment. It should be finalized in a few days, and
it then will be posted on www. The cable data base for the BPMs
was finalized this week as a preparatory step for developing the
BPM procurement packages.
The FEL-server requisition (60 k$) was signed and delivered to
procurement.
Operation of the linear variable differential transformer (LVDT)
VME board was successfully demonstrated. This is a position sensor
that will be used to monitor the FEL optical-cavity length. The
constituent printed circuit boards (PCBs) were surplus from the
Superconducting Supercollider Project.
The prototype PCBs for the ion-pump power supply arrived and are
being tested.
The Software Group demonstrated the (preliminary) operation of
the latch card used in Argonne National Lab's Advanced Photon
Source (APS) Machine Protection System (MPS). This is one of
two PCBs from APS that will form the backbone of the FEL's MPS.
We finalized the cable data base for the vacuum-system components.
Having done so, we can now finalize the corresponding installation
activities as well as the software requirements for the vacuum
system.
FEL Systems
Injector Reinstallation
Northrop Grumman has completed a finite element analysis of the
high voltage power supply chamber. The design is sound with a
factor of 5 safety factor under test conditions and a factor of
8 under operating conditions. We are still awaiting bids from
fabricators of the clean room and the high voltage power supply.
IR Demo wiggler
All drawings of the wiggler support elements are signed off and
out for bid. Design work is nearly complete for the vacuum chamber.
Layout and detailing of the vacuum chamber support will start
next week.
Optics
Work this week continued on detailing drawings for the optical
transport. Specifically, we are checking drawings for the diagnostic
pick off, and the mirror cans. Work continues to progress on
the collimator and the mirror cassettes. We now have engineering
support to design the optical table stands. Most of the revisions
to mounting hardware for the optical cavity assemblies have been
made and were signed off this week. Work continued on fabrication,
although it was slowed somewhat by the need to fabricate HOM loads
for the FEL cryomodule. We received the IR detectors that will
be used with the diagnostics monochromator. The LabVIEW program
that is supplied with ARC monochromators is undergoing revision
to better adapt it to our needs. The electronics for the interferometer
length diagnostic went through a redesign, and the new version
is being tested.
Operations/Commissioning
As described above under "Accelerator Systems", operations/commissioning
activities focused on supporting the closeout of the Dipole Magnet
Review and also on exploring questions related to operation of
the dipole magnets.
Facility
Work this week involved installing lighting systems and services
piping in the tunnel area. By the end of the week nearly half
of the lighting fixtures had been hung and welding was underway
on the cooling water piping. The steel framework staging was
started for the second floor of the building. That work is expected
to get into full swing next week. The base for the utilities
building was poured and that area was in the process of being
prepared for equipment installation.