Newsgroups: sci.physics.plasma
From IRBY@CMOD2.PFC.MIT.EDU Tue Apr 23 19:53:20 1996
From: IRBY@CMOD2.PFC.MIT.EDU
Organization: MIT
Subject: Alcator C-MOD Weekly Highlights

Alcator C-MOD Weekly Highlights
April 23, 1996

Frederick Hawthorne and Rachel Watson of UCLA have completed
a preliminary analysis of the boron deposits found on the outer divertor
cover plates. Using NMR techniques, they have found mostly salt-like
compounds, some boric oxides, and small amounts of boric acid. Analysis
continues on wipes made of the first wall tiles and outer vessel wall.
The camera fixture attached to the inner wall has now been used
to document in-vessel hardware including the upper and lower inner divertor,
the outer divertor, diagnostics, ports, and the outer vessel wall. This
information will be used to help plan diagnostic relocations and additions
as we add new major upgrades such as the RF antenna, diagnostic neutral beam,
and divertor cryopump. We are now carefully documenting the outer divertor
before it is removed. Changes will be made to the outer divertor support
structure in preparation for higher plasma current operation during
the summer run.
Work on several engineering systems continued this week in preparation
for both the next run period and longer term goals. The flywheel bearings
are now back in-house and are being installed. Re-assembly of the
alternator and associated systems continues. Cold gas tests of the TF
cooling are being conducted in preparation for installation of the new TF
cooling control valves. TORVAC control racks are being readied for
relocation to the new west diagnostic stand extension. In addition, cabling
for several diagnostic racks is also being measured for extension or
replacement in preparation for relocation. These changes will provide room
for the LN2 and LHe dewers needed for the prototype cryopump, as well as
space for the RF components needed to feed the new RF antenna.
The 110/208 VAC control power has been supplied to the RF switchgear
and testing of the breaker is set to begin this week. Requests for quotes
have been issued for installation of the 13.8 KVAC and high voltage DC stress
cones needed to supply power to the new RF transmitters. Layout of the
control cabinet has been completed, and wiring between the FMIT drivers and
the control cabinet is being planned.
Analysis of data from the last run campaign continues. As part
of work being carried out by Francesca Bombarda, Stefano Migliuolo,
and Bruno Coppi, aimed at the characterization of C-MOD sawteeth as
a function of plasma parameters, some preliminary results have
been obtained. For example, the sawtooth period is observed to be
independent of density. In ohmic plasmas, at 5.3 T and 0.8 MA, the sawtooth
period is about 5 ms, over a density range of 0.7 to 4.5X10^20/m^3. The
sawtooth period increases with power, as can be clearly observed when RF
heating is applied, and also scales linearly with stored energy. This
correlation is observed over a wide range of stored energy (20-200 KJ), and
includes low and high current L-mode, pre- and post-boronization,
ohmic and RF, and H-modes discharges.
Joe Snipes attended the 4th ITER Confinement Database and Modelling
Expert Group Workshop held in Moscow. He presented talks on 1) the C-MOD
results on the H-mode threshold, 2) the proposed joint experiment
at fixed density and toroidal field with JET, JT-60U, and ASDEX-Upgrade
to determine the size scaling of the H-mode threshold, and 3) the C-MOD
H-mode confinement results. The meeting was intended as an update
of the analysis of the ITER confinement and H-mode threshold databases as well
as the profile database that is being used to test models of both H and L-mode
confinement. It was attended by about 20 physicists from most of the major
tokamaks around the world (Alcator C-MOD, ASDEX-Upgrade, DIII-D, JET, JFT-2M,
JT-60U, PBX-M, T-10, TCV, and TFTR) as well as a number of modellers. The
Alcator C-MOD data were particularly well received by the group because C-MOD
operates in a quite different size and toroidal field range than the other
tokamaks. Inclusion of C-MOD data increases the range of the experimental
measurements, and provides a good test of the extrapolation of the existing
scalings. In particular, the C-MOD threshold data challenges the empirical
scaling with toroidal field and size. Similarly, the C-MOD H-mode confinement
data lies significantly above the published scalings, and appears to indicate
a weaker size dependence (or stronger field scaling) than previously expected.
Bob Granetz is in Japan attending the 4th ITER Physics Expert
Group Meeting on Disruptions, Plasma Control, and MHD. He is presenting
talks on C-MOD halo current and killer pellet results.