Newsgroups: sci.physics.plasma
From: WOLFE@CMOD2.PFC.MIT.EDU
Organization: MIT
Subject: Alcator C-MOD Weekly Highlights

Alcator C-MOD Weekly Highlights
Nov. 28, 1994

Plasma operation is continuing on Alcator C-MOD. Due to the holiday, only
three run days were scheduled last week. Nevertheless, excellent progress was
made.

Following Monday's run, during which standard tokamak plasmas were produced in
the inner-wall limiter configuration, we began setting up diverted discharges.
On Tuesday, 800 kA lower single null diverted discharges similar to those run
during June of this year were re-established. The re-start mini-proposal was
declared completed.

Wednesday's run was devoted to a new mini-proposal (MP#065), to develop
orthogonal control techniques for the plasma shape. The plasmas were lower
single null, similar to those run on Tuesday. Good progress was made on this
task. The orthogonal controllers for plasma current and R and Z centroid were
installed and tuned up. Those for inner gap, and R and Z location of the
active x-point were installed and seem to work correctly, but not completely
optimized. The direct current control on all PF coils (except for EF4) was
turned off during the portion of the shot for which the shape controlers were
active. Controllers for the position of the upper x-point were installed, but
not yet tuned up. This needs to be completed and a more thorough exercising of
the control to demonstrate orthogonal behavior must be carried out to complete
this experiment. Once this is accomplished, development of new equilibria
should be greatly simplified.

In the course of Wednesday's run, several ohmic H-mode transitions were
obtained. These shots were well diverted with B=5.3 Tesla and density greater
than 1e20/m^3. No special wall conditioning had been done prior to these
discharges.

Several disruptions were produced during this week's operation. The new halo
current diagnostics, including the re-designed divertor shunts and the new
segmented toroidal rogowski coil, are operational and the data is being
analyzed. Initial indications point to a significant n=1 component in the halo
currents.

Diagnostics are continuing to come on-line. The bolometer arrays, Moly monitor,
and the McPherson UV spectrometer are now operational. The ECE Michaelson
electron temperature diagnostic was on-line for plasma operation, with
calibration being carried out today.

Progress is also being made on the ICRF system. The #1 transmitter has
produced 2 MW for a one second pulse into a dummy load. The external resonant
loops for both the D- and E-port antennas have been installed.

As part of our ongoing collaboration with scientists from Los Alamos National
Laboratory, Glenn Wurden visited C-Mod from Nov. 20 through Nov. 23. He came
to discuss the details of an experiments planned for CY '95 in which a fast
CCD camera will be used used to view various phenomena, e.g. pellet ablation,
disruptions, etc. In addition, for this visit he brought an IR TV camera
which we set up to view the inner wall. In two days of running we were able to
observe the following: 1) During the shot there was plasma light emitted in
the wavelength band which the camera viewed (~2 to 3.5 microns). This is
probably due to atomic hydrogen emission. 2) A few seconds after the shot the
temperature of inner wall tiles increased by a few degrees C. While the
magnitude is understandable, the delay is still not understood. 3) The IR TV
images showed clearly a tile which we knew to have poorer thermal contact with
the wall. They also showed that the leading edges of the tiles were hotter
than the rest of the surface.

Ben Welch is visiting this week from the University of Maryland. His high
resolution spectroscopy diagnostic is now installed and operational.

Dr. Earl Marmar is in Russia this week for a meeting of the ITER diagnostics
group.