MEMORANDUM
To: Distribution
From: F. Dylla
Subject: Monthly Report IR Demo FEL Upgrade and Commissioning
Project, Nov. 1997
Date: December 18, 1997
Management
November 1997 was the fourth month for the $3.7M IR Demo FEL Upgrade
and Commissioning project. Cost and schedule performance are
described in the accompanying "Performance Assessment"
report by Gordon Smith. A summary of the technical progress of
the remaining three open cost accounts is given below.
CA 221: Scaleable Optical Cavity
A survey of existing coating capabilities as regards S and P wave
losses at 54.7 degrees was completed. Owing to the unusual angle
few companies are interested in quoting on the coating despite
the relatively easy wavelength. Discussions continue with China
Lake regarding providing a designed coating that will meet our
requirements.
CA 321 Upgrade Cryomodule System
All eight cavities have been through at least one round of processing
and testing. The achieved gradients for all of these cavities
exceed 10 MV/m. Given that the cavity-pair assemblies are not
needed for cryomodule assembly until later in the fiscal year,
additional processing and testing will be done on the upgrade
cryomodule cavities to push the maximum gradients. Components
for the end-dish bellows assemblies have been machined. A majority
of the HOM components and other small components needed for the
cryomodule assembly have been received. Successful SRF commissioning
of the IR Demo injector cryounit and linac cryomodule (as noted
in the commissioning section below) have benchmarked the design
changes we made to the standard CEBAF cryomodule design for use
in the FEL cryomodule.
CA 421: Commissioning Preparation
This account was closed to further obligations last month (October).
By January we expect the remaining cost obligations to be closed
out including completion of the delivery of corrector magnets
and components for the analog moniotoring system.
CA 521: IR FEL Commissioning
Commissioning activities focused principally on completing the
injector, taking tuneup beam from the photocathode to the injection-line
dump, and getting the cryomodule ready to accept beam. SRF and
RF commissioning of the cryounit was completed. Nominal operating
cavity gradients are 12 MV/m for the entrance cavity and 8.5 MV/m
for the exit cavity, with unloaded Q at 5x10^9. By month's end
we were routinely running beam through the injector and into its
dump with average current ranging up to roughly 1 µA and
with bunch charges of order 1 pC. Using the first dipole magnet,
we measured the electron-beam momentum to be 7.5 MeV/c, to within
±10%, with the two cryounit cavities operating on crest.
This value is lower than what was expected based on the nominal
accelerating gradients of the cavities measured during the SRF
commissioning process; however, we found the cause to be an incorrectly
calibrated control- system screen that indicated artificially
high cavity gradients. Electron-beam profiles on the viewers
were consistent with simulation (PARMELA) results. (Note: After
recalibrating the screens, we measured on the evening of 2 Dec.
97 the electron-beam momentum to be 9.6 MeV/c, to within ±10%,
with the two cryounit cavities operating on crest, a value consistent
with expectations.)
Both SRF and RF commissioning of the cryomodule was completed,
resulting in a total available accelerating voltage of > 47
MV.
FEL INSTALLATION
Installation highlights in November included:
Completing all hardware installation from the photocathode to
the energy-recovery dump in preparation for running beam not only
through the injector, but also through the linac cryomodule (slated
for early December).
Nearly completing hardware installation for the full straight-ahead
machine. By month's end some vacuum chambers upstream and downstream
of the wiggler still needed to be installed, as did one of the
injection/extraction (DV) dipoles, raster magnets on the straight-ahead
dump line, and shielding for this dump. We decided to install
CEBAF-spare air-core corrector magnets as a temporary measure
to enable running with tune-up beam as we await delivery of the
"real" air- core correctors from the vendor.
The wiggler vacuum chamber was aligned and the electron beam viewers
in the wiggler fiducialized with respect to the beam axis. Verifications
of the physical stability were completed successfully. Secondary
alignment apertures were established to permit alignment of the
system without breaking electron beam vacuum. Clean hoods were
constructed over the tables and the optical mounts and vacuum
hardware placed in preliminary positions on their respective
optical tables.
Making substantial progress toward installing the recirculation
arcs. Three of the four DX arc dipole magnets were given their
initial alignment as the first step of their installation. The
first 180-degree arc dipole (DY) was installed in the east arc
(minus its coil assembly) to allow vacuum chamber fit-up operations
to proceed. The second 180-degree arc dipole (with a completed
coil assembly) was installed in its magnetic measurement test
stand which is now operational.
The fabrication of three high power (50 kW) warm window assemblies was completed in November. These windows will be installed in the injector cryounit in January during the CHL shut-down.