Management
June 1998 was the eleventh month for the $3.7M
IR Demo Upgrade and Commissioning project. Cost and schedule
performance are described in the accompanying Performance Assessment
report by Gordon Smith. Highlights for the month include: attainment
of "first light" from the FEL on June 15, 1998 and attainment
of an average power record for FELs of 155 watts, just two days
later on June 17, 1998.
CA 221: Scaleable Optical Cavity
June saw the completion of the commissioning
of the FEL systems when first lasing was produced on June 15 at
20:25. Initial lasing was in pulsed mode which indicated that
operation was strong and insensitive to alignments, etc. This
was confirmed in subsequent runs the following days when first
50 then 155 W of CW lasing power at 5 microns was produced using
the 98% outcoupler designed for 10 W operation. This output is
more than 15 times the previous record for any FEL.
Mirror coating measurements by China Lake
had set an upper bound on mirror absorption of 0.001 Our measurements
suggest that it is roughly 5 times lower than that, truly excellent
performance for the 5 micron band. We are in the process of comparing
FEL performance to our models. If anything, early data suggests
the laser is operating better than our model predicts.
We have taken spectral data at various cavity
lengths and have effectively increased outcoupling by operating
at lower linac repetition rates than the cavity round trip time.
Lasing with more than 16% outcoupling has been observed. Diagnostics
commissioned include the monochrometer with both a boxcar and
a lock-in amplifier interface, the pyroelectric camera, and the
power meters. Harmonic radiation was observed by eye and camera
out to the 11th harmonic in the yellow/green.
Work in the coming month will be to install
the high power mirrors and see what level of power can be produced
and also to install and align an array of user equipment in preparation
for the first user experiments.
CA 321: Upgrade Cryomodule System
The second set of four cavities were vertically
tested. As a result of additional processing cycles, all cavities
for the upgrade cryomodule have been pushed above 12 MV/M (vs.
8 MV/M specifications). The dog leg coupler window test stands
were fabricated and leaked checked. The first two windows have
been placed on the test stands and are ready for testing for cryogenic
losses.
HOM ceramics were received and the fabrication
of all the loads have been completed. Testing of these loads
will be accomplished next month.
CA 421: Commissioning Preparations
This account has been closed to further obligations
since October.
CA 521: FEL COMMISSIONING
We worked through the first half of the month
to obtain the electron-beam quality required for lasing. On 13
Jun 98, a Saturday, we installed the wiggler. On Monday afternoon,
15 Jun 98, we turned on the machine and began lasing at low power
just five hours later. We then lased at tens of watts on Tuesday,
and on Wednesday at 1250 we achieved 100 W cw at 4.95 µm.
Ultimately that same day we achieved 155 W cw briefly and 150
W cw stably, running at the latter power level for a time approaching
an hour. The whole machine ran stably. By week's end, we were
delivering well over 100 watts cw stably into the Optical Control
Room located upstairs in the FEL Facility.
Encouraged by the success, we resolved to
try for kilowatt lasing this summer. In turn, we needed to finish
all remaining details on the machine for high power operations.
To take full advantage of the availability of people, we did
not run electron beam during the remainder of the month. Instead,
we used the time to complete numerous installation activities,
foremost of which was the entire vacuum system of the machine.
Part of the vacuum activities was to replace eight problematic
valves. Another activity centered on attempting to rejuvenate
the photocathode in situ by way of high-voltage processing and
heat cleaning. At month's end, the cathode's photoresponse appeared
to be marginal, and plans were being made toward another rejuvenation
attempt.
We began planning how to attempt kilowatt
operation this summer while interleaving the associated commissioning
activities with a nominal effort to support user experiments.
A considerable amount of progress was made toward developing
procedures that support recirculation and energy recovery, including
particularly the "Lase with Energy Recovery Metaprocedure"
and "RF Stability during Energy Recovery".
Replacing eight beamline valves because of
concerns about their reliability; modifying the beamline leading
to the injector dump to suppress scraping at our highest average
currents (4-5 mA); and placing the entire machine under vacuum
for the first time.
Upgrading the drive-laser pulse controller
to permit operation at 37.4 MHz in support of kW-level lasing,
as well as rejuvenating the photocathode.
Installing a synchrotron radiation monitor
and limit switches on the associated viewers in both of the 180-degree
dipole magnets, four additional DF trim dipoles, two DG and four
DC trim dipoles in the recirculation arcs, and the last remaining
skew quadrupole in the injector.
Changing the viewer flag for one of the wiggler
viewers from graphite to beryllium; installing both of the Happek
interferometric bunch-length monitors; and installing all cabling
for the beam-loss monitors in the recirculation loop.
Testing additional ceramic windows with the
50 kW klystron system; the tests were successful.
Completing instrumentation of the Optical
Control Room, to include its Laser Safety System (LSS); certifying
the LSS configuration for the user laboratories; and progressing
with the setup of both the Polymer Lab and the Metals Lab in the
FEL Facility.