MEMORANDUM
To: J. Cook, D. Helms, W. Skinner
cc: Division (M7), FEL Coordination Group
From: F. Dylla
Subject: IR Demo Project Weekly Report, December 1-5, 1997
Date: December 5, 1997
Management:
Highlights for the week include: confirmation of the acceleration
capabilities of the injector quarter-unit to be 9.6 MeV/c; readiness
for low current beam operation through the linac cryomodule until
beam operations were suspended late Tuesday due to a valve failure;
and good progress on preparing the remainder of the first light
beamline for vacuum pumping.
Preparations were made for next week's visit by Congressional
staffers from the Energy and Water Committee on Tuesday, Dec.
9, and by MTAC on Dec. 9-10.
Discussions continued with the management of NASA Langley Research
Center concerning a joint presentation to the NASA Chief Technologist
on Dec. 15th on a proposed NASA competition for research proposals
to use the IR FEL.
Monthly progress reports that were completed last week for both
the construction and upgrade projects for October 1997 were distributed
to the Navy and DOE Program Offices on Monday, Dec. 1.
Installation Activities
The RF software was upgraded this week to fix several bugs. A
newly installed code from a different application was consuming
too much computer bandwidth. The RF code faulted itself for being
too slow. The RF code is being tested again today with additional
work set next week.
SRF commissioning is expected to be finished this evening with
the cavity Q measurements. RF commissioning will be finished
when the final coefficients are determined. (More details in
the commissioning report below.)
All vacuum connections for the machine through the 1G, recirculation
dump, have been made and pumped down. The vacuum chambers for
the 2F, optical section, and 2G, straight ahead dump, are completed
and installed. Pumpdown is planned for next week. LCW and instrument
air connections have been made to all installed equipment. The
shield stand for the 2G dump is installed.
The girders have been installed for both arcs. Mechanical fit-up
for the 180° vacuum chambers is underway. Three DX magnets
for the arcs have been installed.
The wiggler viewers have been checked several times using several
methods and have been shown to be reproducibly aligned to within
100 microns of the axis defined by the first and last quadrupoles
on the wiggler girder. Apertures have been set up on the optical
benches for the optical cavity which define this aperture in the
absence of accessibility to the quadrupole surfaces. The vacuum
chambers around the wiggler were successfully installed and the
viewer positions rechecked. Viewer assemblies were installed.
It was found that one of the sets of lenses for these assemblies
was the wrong focal length. It was possible to move components
around to compensate for this and get an image of viewers one
and two. The third awaits wiring of the power for the camera
which should be done this weekend. The position of the resonator
mirror mounts was measured and found to be within approximately
one mm or less of the axis defined by the quadrupoles. This is
2% of the mirror aperture and is quite adequate.
Commissioning Activities
We ran tune-up beam to the injector dump at currents up to about
1µA, and measured momenta ranging up to 9.6 Mev/c to within
±10% accuracy, at which both cryounit cavities were operating
on crest. Accordingly, momentum measurements were consistent
with expectations given the cryounit cavity gradients established
during SRF commissioning. The discrepancy in beam momentum versus
SRF gradient that was reported two weeks earlier was traced to
a 3 dB miscalibration, with the consequence that the gradients
displayed on the screen in the control room are a factor of two
off. The cause remains uncertain, but it is a simple matter to
correct the control screen readouts. Cavity gradients reported
from SRF commissioning of the cryounit were verified to be correct.
On 2 Dec. 97 we were preparing to put beam into the cryomodule,
precisely on schedule. Upon being unlocked, the vacuum valve
preceding the cryomodule stuck in the open position, leaving the
cryomodule vulnerable to vacuum leaks in the upstream beamline.
At this point beam operations were suspended. Concerted attempts
to unstick the valve failed, and more intrusive techniques were
rejected for fear of introducing a vacuum leak through the valve.
The valve must be replaced, and there is a day-for-day slip in
the commissioning schedule as we await replacement. Resumption
of beam operations is projected for swing shift next Friday, 12
Dec. 97.
The "window of opportunity" presented by seizure of
the valve is being used to measure the unloaded Qs of the cryounit
cavities, an activity that began last night and will be completed
tonight.
Plans for replacing the stuck valve are as follows: Two new valves
are on order from VAT in Switzerland, and they are likely to be
shipped today (but a small possibility exists that they would
not be shipped until next Friday). Once we receive them, probably
next Wednesday, we'll need to dismantle them, clean them, reassemble
them, and put them through several cycles prior to installation,
now projected for next Friday, 12 Dec. 97. Cryomodule warmup
requires care and ideally should be done slowly, so plans are
to begin warmup after finishing the unloaded Q measurements tonight.
Cooldown will be rapid, projected to start the evening of 12 Dec.
97 and be complete to 2K 12-16 hours later, making the cryomodule
ready to accept beam next Saturday.
A revised shift schedule was developed leading into Christmas. It provides for both running tune-up beam to the straight-ahead dump and generating 60 pC bunch charges (per first-light requirements) with which to check out emittance and bunch-length diagnostics.