Newsgroups: sci.physics.plasma
From WOLFE@CMOD2.PFC.MIT.EDU Tue Apr 18 18:01:57 1995
From: WOLFE@CMOD2.PFC.MIT.EDU
Organization: MIT
Subject: Alcator C-MOD Weekly Highlights

Alcator C-MOD Weekly Highlights
April 18, 1995

Plasma operations continued on Alcator C-MOD last week. This week completed
the two-week reversed field (and current) operation. Four run days were
scheduled and completed last week. Experiments included measurements of
asymmetries in neutral populations, ICRF L-mode scaling, H-mode threshold
determination with the ion grad-B drift away from the x-point, and
measurements of impurity transport and plume behavior using the capillary tube
localized gas-injection system.

Measurements of asymmetries in charge exchange flux, as measured by passive
neutral particle analyzers, and in core neutral population, as determined from
emission from states of hydrogen-like Ar populated by charge-exchange
recombination, were measured in the reversed field configuration. Most of the
data were taken with the usual lower single null orientation, with a few shots
obtained with an upper x-point; the ion grad-B drift direction was upward. The
previously observed asymmetry in core neutral density appeared to remain
correlated with the x-point orientation, independent of the grad-B drift. The
up-down asymmetry in impurity density, on the other hand, was observed to
reverse with the reversed field.

ICRF heating experiments were continued, with additional data on L-mode
confinement scaling being obtained. Attempts to reach the H-mode threshold
with the ion drift away from the x-point were unsuccessful, with a lower
bound of P/nBS > 0.06 being established for these experiments.

Studies of injected impurities using the capillary tube system were carried out
for both upper and lower null equilibria in the reverse-field configuration.
Impurities were injected at the inner wall and at the divertor, with spatial
spreading (plumes) monitored by CCD cameras. These data will be used to
determine plasma flows in the SOL. Impurity screening was studied using CH4,
He, and Ar. Successful measurements of the spatial distributions of CII, CIII,
(or HeI and HeII) were made. The neutral species H0 and HeI were
approximately symmetric. The plumes from impurity ions were almost always
towards the divertor target, i.e. they reversed when the X-point was moved from
lower to upper. Exceptions were that the plume went away from the x-point
during current rampdown, when there was a very large CH4 injection and at high
density. Measurements were taken successfully with the Fast Scanning Probe
under most conditions of density and impurity puffing and with both upper and
lower X-point. This should allow us to extrapolate the ne and Te profile
conditions to the positions where the impurities were puffed.

Steve Golovato participated in discussions of the TPX ICRF antenna and outboard
limiter design. He also took part in a review of the ORNL RF Technology Program.
Earl Marmar was in San Diego participating in an ITER Home Team Physics Design
Review.

C-MOD is now entering a scheduled maintenance week; no operations are
scheduled during the week beginning April 17.