Newsgroups: sci.physics.plasma
From WOLFE@CMOD2.PFC.MIT.EDU Tue Feb 6 11:56:13 1996
From: WOLFE@CMOD2.PFC.MIT.EDU
Organization: MIT
Subject: Alcator C-MOD Weekly Highlights

Alcator C-MOD Weekly Highlights
Feb 5, 1996

Plasma operations continued at Alcator C-MOD last week, with four run days
scheduled and completed. A total of 113 plasma shots were produced, at
toroidal fields ranging from 2.6T to 7.9T and plasma currents from 300kA to
1.2MA. Boronization was carried out overnight on Monday, prior to the week's
operation.

Studies of boronized H-mode operation at 5.3T were carried out on Tuesday,
with only 20 minutes of He discharge cleaning after the boronization.
The first few shots of the day had long H-mode, but the H-factor wasn't high.
It took several shots to get good H-factors. Sweeping of the strike point was
implemented to get better profiles at the divertor and to spread the heat
flux. Profile scans at "low" and "high" density were performed at 1.1MA and
0.8MA. The "low" density scan at 1.1MA was not completed because of repeated
disruptions (q was just above 3 because the inner and outer gaps were
relatively large). Some data were also taken at low density at 1.0MA.

D(He3) heating at 7.9T was the topic on Wednesday. Coarse density and minority
concentration scans were carried out at 1MA, and a profile scan carried out for
the optimum heating condition. At higher than optimum concentrations, off-axis
electron heating was observed. This effect is predicted by theory from
direct electron absorption from the mode converted Bernstein wave at high
He3 fraction. One shot at higher current (1.2MA) was taken, and confinement
and stored energy increased, as expected.

An L-mode rho-star scaling experiment(varying Bt with n and P varied
simultaneously to maintain nu-star and beta constant, while plasma current was
scaled to give constant q) was carried out on Thursday. This run was in
support of PhD thesis research, and was a continuation of experiments begun in
December. Shots were taken at 5.3T and 2.6T. Some difficulties were
encountered in matching the parameters of the previous run, which had been
carried out before we began boronization. In particular, it proved difficult
to run at the lowest densities called for in the protocol, and one of the 5.3T
conditions ended up transitioning to H-mode. Nevertheless, some useful data
was obtained, and this experiment will be continued. In addition to the L-mode
data, a useful point for an H-mode rho-star scaling experiment was identified
at B=2.6T and Ip=550kA (q~3.3). The 5.3 T points in this run employed our
usual D(H) minority heating, while the 2.6T cases include both ohmic and
second harmonic H-minority heating, also with D as the majority species.

Friday's run revisited the question of the relative screening in limiter and
diverted discharges, to determine how the results were affected by the
presence of boronized walls. N2 was injected as a non-recycling impurity into
a series of limited plasmas from different spatial locations. Several diverted
shots and background (no N2 puff) shots were included as baselines.

Dr. Charles Skinner of PPPL was visiting C-MOD last week to work on his
optical Fabry-Perot diagnostic and to participate in the impurity screening
experiment on Friday.

Horacio Lamela, Pablo Acedo, and Gwillerono Carpintero from Carlos III
University, Madrid, Spain are visiting this week to discuss CO2 interferometry.

A review of the Alcator Program by the Alcator C-MOD Advisory Committee will
be held at M.I.T. on March 6-7, 1996. Time is being reserved on the agenda for
present and prospective new collaborators to describe their results and future
plans. Interested parties should contact Steve Wolfe (wolfe@pfc.mit.edu) by
Friday, February 16, 1996, providing a brief outline of the material to be
presented and the amount of time requested.