Newsgroups: sci.physics.plasma
From WOLFE@CMOD2.PFC.MIT.EDU Tue Mar 7 09:12:38 1995
From: WOLFE@CMOD2.PFC.MIT.EDU
Organization: MIT
Subject: Alcator C-MOD Weekly Highlights

Alcator C-MOD Weekly Highlights
March 6, 1995

Alcator C-MOD plasma operations resumed last week after a scheduled one-week
maintenance period. Four runs were scheduled, but the first, on Tuesday, had
to be cut short due to a computer problem. Experiments scheduled and completed
included a study of heating and confinement in ICRF L-mode plasmas; the C-MOD
portion of a joint investigation with DIII-D on non-dimensionally identical
discharges; and a continuation of the study of transport and screening of
non-recycling impurities, this time using methane as the injected impurity.

One and a half runs were devoted to getting the C-MOD data for a direct
comparison of Alcator C-MOD and DIII-D running at identical non-dimensional
parameters (rho*, beta, nu*, q, kappa, etc.). For C-MOD the dimensional
parameters chosen for this comparison were R= .67m, a = .22m, kappa = 1.65,
Ip=1.02, Bt=5.3T with a SNB equilibrium; inner and outer gaps were around 1cm.
Power scans were carried out at two densities, nebar ~ 1.5 and 2.6e20.
Despite some difficulties with the D-port ICRF transmission line, and some
problems associated with wall conditioning related to the previous week's
vent, these experiments were successfully completed. Dr. Jim DeBoo from DIII-D
participated in these experiments at MIT, and will be directing the
corresponding experiments at GA.

L-mode heating experiments were carried out at several densities up to 3e20
and currents up to 1.2MA. H-mode transitions were observed at powers above
1MW. Good L-mode power scans to higher power will have to wait for the reverse
field run next month.

Studies of non-recycling impurities were continued, using CH4 as the injected
gas. The goals were (1) to study trace impurity screening for comparison with
N2,Ar, Ne; and (2) raise the CH4 levels to try and maximize the impurity
radiation in the SOL relative to that in the core plasma. Results were similar
to earlier experiments using N2. No immediate carbon signal was observed in
the divertor when the methane was injected at the midplane. For large puffs,
divertor detachment was observed.

Royce Sayer (ORNL) and Steve Jardin (PPPL) visited MIT for discussions related
to their collaboration on halo currents and disruptions. They will be using
the TSC code to model disruption behavior in C-MOD. Sayer presented the
results of several scoping runs based on data from a typical midplane
disruption. Several shots were identified for analysis during the next stage
of the collaboration, including both midplane disruptions and VDE's.

Dr. Rob Pinsker from the DIII-D Group continued his visit, working all week
with the C-MOD ICRF group.