Newsgroups: sci.physics.plasma
From WOLFE@CMOD2.PFC.MIT.EDU Tue Jan 24 12:53:44 1995
From: WOLFE@CMOD2.PFC.MIT.EDU
Organization: MIT
Subject: Alcator C-MOD Weekly Highlights

ALCATOR C-MOD Weekly Highlights
Jan. 23, 1995

Alcator C-MOD is continuing plasma operations. Three runs were scheduled and
completed this week. The major highlight of the week was the successful
coupling of 3.5MW into the plasma (approximately 4 MW at the source). Other
experiments included measurements on neutral density profiles in the plasma
core, experiments on impurity transport in the divertor,and pellet injection
in combination with RF heating. In addition, calibrations were carried out for
the divertor neutral pressure gauge and the NINJA capillary gas puff system
as well as the B-side valve used for impurity puffing experiments.

Up to 3.5MW of ICRF was coupled to the plasma during piggy-back operation on
Wednesday. This power level, corresponding to approximately 4MW at the source,
is the nominal maximum power level for the current campaign, using both D-port
and E-port antennas. Central electron and ion temperatures in the 4-5 keV
range were obtained at line-average density of 1e20/m3 and a plasma current of
800kA. The stored energy in the plasma exceeded 100kJ for the first time.
Preliminary assessments indicate the confinement was consistent with standard
L-mode scaling.

Heating experiments at the 3MW level continued on Friday, at higher density of
1.3 and 1.7e20. Virtually all shots with high RF power (two antennas) at
these densities transitioned into H-mode. We were able to sustain the H-mode
(ELM-free then becoming ELMy) for the duration of high power RF (200msec).
Following the density rise in the ELM-free period, a new steady-state density
level is maintained, with strong ELM activity, until the RF pulse is terminated.
One shot had a Li pellet 50msec injected prior to the RF pulse, and a record
neutron rate (almost 1e14/sec) was obtained during the "PEP" phase when the
density profile is highly peaked.

On Thursday, an investigation of impurity screening was carried out, using
trace impurities (Ne, He, and Ar) puffed from capillary tubes in various
poloidal locations. Comparisons were made for puffing at the inner wall, the
private flux zone of the divertor, and the outer SOL. Preliminary analysis
indicates the core neon signal, e.g., varies by less than a factor of two for
the different source locations.

Measurements of neutral density profiles, employing the technique of looking at
charge exchange recombination of highly ionized Argon (MP#049A), were also
carried out. The previously observed up-down asymmetry in the neutral density
was confirmed, but a more quantitative assessment of the neutral profile was
not possible due to the limited number of satisfactory shots.

A Review of the C-MOD program was held at MIT on Tuesday and Wednesday.
Participants from D.o.E. (Tuesday only) were Don Priester and Milt Johnson;
attending as members of the C-MOD Advisory panel were G. Nielson, P. Edmonds,
S. Allen, R. Hawryluk, and F. Perkins. Presentations on recent C-MOD results
and future plans were made by I. Hutchinson, B. Lipschultz, M. Porkolab, R.
Wilson (PPPL), M. Greenwald, S. Wolfe, R. Granetz, J. Irby, D. Gwinn, and E.
Marmar.