Newsgroups: sci.physics.plasma
From MARMAR@CMOD2.PFC.MIT.EDU Tue Dec 26 19:19:56 1995
From: MARMAR@CMOD2.PFC.MIT.EDU
Organization: MIT
Subject: Alcator C-Mod Weekly Highlights -- December 26,1995

Alcator C-Mod Weekly Highlights
Dec 26, 1995

The operating campaign continued last week, with 4 runs scheduled and 3
completed. The run on Wednesday, Dec. 20, was cancelled because of a
snowstorm. Two of the three runs had graduate students as Session Leaders,
and were in direct support of their thesis research.

Rho-star scaling (MP 122A) was investigated on Monday, Dec. 18. Discharges
were operated at toroidal fields of 2.6, 3.5 and 5.3 Tesla, making use of
the new capability to control the TF waveform from the Hybrid computer.
Four different groups of parameters were run, with 30 good plasmas for the
mini-proposal, plus one fiducial shot. Analysis of the results is underway.

On Tuesday, Dec. 19, emission plumes resulting from injection of nitrogen
and helium gas at various locations were studied (MP 128). These plumes are
a measure of plsama flow in the plasma edge. This was a very
successful run, yielding many interesting results. N-II, N-III, and He-II
plumes were observed over a range of plasma densities and recorded during
nitrogen and helium injection at the inner-wall midplane. Additionally,
bright N-II plumes were observed during nitrogen injection on the outer
divertor, inner divertor, and outer A-B limiter. In all cases, the plumes
were observed to flow in the expected direction (towards the strike point).
The nitrogen puffs were observed to be somewhat perturbative (ideally these
injections should be `trace'), inducing detachment in the outer divertor
even during low density shots. The helium puffs were also perturbative; a
fairly large flow rate was needed to observe the He-II light, so that the
helium puffs contributed to the fueling of the plasma. While the N-II and
He-II emissions were bright enough to observe well, the N-III emission was
faint. Using the Chromex spectrograph, a bright N-I line (868 nm) was
observed; a filter at that wavelength will be ordered to observe N-I
emission plumes in the future. There was also good success in obtaining
Fast Scanning Probe profiles during the run. Including 1 fiducial, there
were 34 good plasmas produced.

The run on Thursday, Dec. 21, was devoted to Fast Current Ramps (MP 126) and
an initial scoping of ICRF reverse shear mode (MP 125 A). This was
primarily a discharge development run; many of the shots exhibited early
vertical instabilities (and disruptions) and hollow temperature profiles.
Interestingly, one fiducial shot also exhibited vertical instability. The
run was successful in demonstrating the ability to couple high power RF
during the initial current ramp, starting as early as 100 msec after plasma
initiation.

The two weeks from December 25, 1995 through January 5, 1996 are scheduled
for maintenance.

Arrangements have been finalized for Dr. H.G. Esser, from the Institut fur
Plasmaphysik, Julich, to visit MIT in early January. Dr. Esser will
participate in our first boronization experiments.

Yuichi Takase and Earl Marmar were in Princeton last week as members of the
TFTR Program Advisory Committee. Dr. Marmar also attended the first meeting
of the FEAC SciCom sub-panel, held in San Diego. SciCom will be advising
the Strategic Planning Subcommittee of FEAC on scientific priorities and
directions for the Magnetic Fusion Energy Program.