From:
irby@PSFC.MIT.EDU
Reply-To: IRBY@PSFC.MIT.EDU
Subject: Alcator C-Mod
Weekly Highlights
Newsgroups: sci.physics.plasma
Organization:
MIT
Alcator
C-Mod Weekly Highlights
June
8, 2001
Alcator C-Mod was in operation four days this
week. Very good progress was
made
conditioning both the machine and the ICRF antennas. Up to 3.7 MW
of ICRF power was coupled into the plasma,
though heating efficiency was
low because the hydrogen fraction was still
high. However, conditioning
of the
machine and antennas is now sufficient for boronization to take place
early
next week.
Physics
-------
Time has been
devoted during two runs for ASDEX shape development.
This experiment will
produce equivalently shaped plasmas on C-Mod as on ASDEX
Upgrade and
attempt to match dimensionless parameters v*, rho* and beta near
the edge
of the plasma (the H-mode pedestal region), both at the L-H
transition and
in the fully developed H-mode. We can
now generate plasmas
needed for the ASDEX/C-Mod scaling studies.
Bill
Dorland from the University of Maryland visited for a day and a half to
help
bring up the parallel version of the gyrokinetic stability code, gs2,
on
our newly built Beowulf cluster. We
expect the cluster to achieve
computational rates of over 20 Gflops.
ICRF
Systems
------------
All calibration factors have now been
obtained for the J-Port antenna needed
to operate with [0,pi,0,pi]
phasing. The maximum injected power
thus far
from the antenna is ~1.7
MW for ~50 ms. This power level was
limited only
by the antenna conditioning time and will improve with
operation time and
boronization.
The new optical monitoring diagnostics of the J-port strip lines
detected
signal when the D and E-Port antennas were active. Comparisons with
the voltage data indicate the induced
voltage from D and E-Port antennas
are low when the light signal is detected and high when no light
is observed.
This result suggests that the low induced voltage is
sufficient to initiate
multipactoring.
The induced voltage from D and E-Port antennas will decrease
as the
H/D ratio decreases and absorption improves.
D and E-Port antenna
conditioning has improved greatly during the week.
Approximately 1.25 MW
was obtained from each antenna, or about 2.5 MW total.
The density rise
associated with the RF pulse has been greatly reduced as
the conditioning
improved.
By the end of the run on Friday, several discharges
obtained ~3.7 MW
of coupled power from the D, E, and J-Port antennas for
approximately 100 ms,
and some plasma heating was observed. The heating efficiency will improve
as
the H/D ratio is reduced with machine conditioning and boronization.
On
the first application of high voltage on Wednesday, the FMIT#4
transmitter
crowbarred. Upon
disassembly, one of the by-pass capacitors on the
driver cavity was found
to have arced. The capacitor was
replaced
and the transmitter was brought back into operation into plasmas
on Friday.
Lower Hybrid MIE Project
------------------------
We
continue to work on the serial fiber optic link and the realtime software
and
hardware needed for phase and amplitude control of the klystrons.
Details
of the C-Mod cell layout of the LHCD launcher and associated
equipment
are being resolved through close communication between
PPPL and C-Mod
personnel. C-Mod and PPPL are also
coordinating the mapping
of klystrons to waveguide components and
developing a convention for signal
names.
The wiring of
transmitter HV control sub-chassis, and Transmitter Protection
System
chassis is proceeding.
DNB
---
The
DNB was baked for three days at a higher temperature than previously in
an
effort to further reduce water contamination of the beam. We will
not know the benefits of the
bake until several days of beam operation have
been completed.
Diagnostics
-----------
Larry
Guttadora continues to check out the
reflectometer upgrade circuits
at PPPL before returning them to MIT.
The
filter tuning for the BES diagnostic was re-calibrated and the
filter
passband was measured using a spectrometer.
This passband
measurements will greatly simplify future
calibrations.
Inner Divertor
--------------
A
stainless steel C-Plate has been received from the vendor and is
undergoing
fitup tests in our divertor mock-up. Tiles, tile support plates, and ribs
are all interlocking
very tightly as intended. The expected
0.020" gap
between tiles, and the fish-scale high points are well
within spec. Delivery
of the
inconel C-Plates needed for the girdle are well into final production
and
should begin arriving in-house over the next few days. The Backing-plates,
being produced by
another vendor, have been delayed by a week.
Difficulties
programming the machining of the upper surface of the
plate were solved by
a visit by MIT personnel early in the week.
Power
Systems
-------------
A problem with the EF2U power supply
during the run on Tuesday was traced to
a failure in the power supply's
auxiliary step-start contactor. The
contactor
was replaced with a spare unit.
We are investigating why the contactor
failed.
Travel
and Visits
-----------------
Justin Burruss, from General
Atomics in San Diego, visited Tom Fredian
and Josh Stillerman last week to
discuss MDSplus and to demonstrate some
relational database applications
he has developed (both web and IDL based)
which could be useful for
viewing the C-Mod databases.
Ron Parker and Jim Irby visited PPPL to
serve on the FIRE Pre-Conceptual
Design Review Committee from July
5-7. Very good progress has been
made
on magnet, divertor, PFCs, vessel, and fueling systems.