Alcator C-MOD Weekly Highlights
				Dec. 5, 1994

Plasma operation is continuing on Alcator C-MOD. Three run days were scheduled
last week, dedicated to two principal mini-proposals and one piggy-back
experiment. The machine operated reliably and all the planned experiments were
substantially completed. Friday was a scheduled off-day, for installation of
the ICRF hardware and diagnostic work. 

Two days were dedicated to completion of MP#065, on the implementation of
orthogonal shape controllers. The purpose of this experiment was to introduce
new controllers (vectors of power supply voltages) for the principal
parameters characterizing the plasma shape, including plasma position, x-point
locations, and inner gap, etc. These controllers are designed such that
application of any one controller affects only a single parameter, and does
not significantly alter the others. This experiment was successful, and the
new controllers will form the basis of future discharge development
activities. This approach is expected to give better control of the
equilibrium and to facilitate the discharge development process for new
configurations, such as slot divertors, etc. 

During the course of these experiments, which used a 5.3Tesla, 850 kA, lower
single null equilibrium, ohmic H-mode transitions were frequently obtained.
These  H-modes exhibited frequent ELMs, and in some cases reached a
quasi-steady state lasting for essentially the whole duration of the flattop
diverted phase of the discharge, around 0.45 sec. Feedback was able to
maintain the density approximately constant at a line-averaged density of
about 1.2e20. 

One day was devoted to a series of reproducible 600kA inner-wall limiter
discharges, for alignment and checkout of the several diagnostic systems,
including the ECE systems and HIREX x-ray spectroscopy. The same controllers
which had been tested on single-null discharges were used to produce these
symmetric limiter equilibria. Shot-to-shot repeatability was excellent. 

RF installation has continued in preparation for ICRF tuning experiments (with
plasma) scheduled for later this week. Connection of the D-port antenna is now
complete. The NINJA divertor gas-puff system has been baked out and
leak-checked, and is ready for operation. The multi-channel Z-meter array has
been installed and calibrated. Other diagnostic systems continue to be 
brought on-line. 

During an attempt on Friday to clear a short on one filament of the fast
neutral pressure gauge in the main chamber, a vacuum leak occurred in the
feedthrough, bringing the torus pressure up to 1e-5 Torr. The machine was
immediately back-filled with helium, the feedthrough and gauge were replaced,
and the machine pumped down again. Bakeout and discharge cleaning were carried
out over the weekend and on the scheduled maintenance day on Monday.  

Earl Marmar participated in the ITER Spectroscopy Working Group meeting in
Moscow last week. Martin Greenwald was in Washington for the ESNET Steering
Committee meeting.