Newsgroups: sci.physics.plasma
From WOLFE@CMOD2.PFC.MIT.EDU Tue Mar 28 12:44:19 1995
From: WOLFE@CMOD2.PFC.MIT.EDU
Organization: MIT
Subject: Alcator C-MOD Weekly Highlights

Alcator C-MOD Weekly Highlights
March 27, 1995

Alcator C-MOD plasma operations continued last week, with four runs scheduled
and completed. A total of 115 successful plasma shots were run during this
time.

Studies of divertor detachment continued on Tuesday. With the outer
strike-point in the nominal position on the vertical target plate, the
(line-averaged) density was raised above 4e20/m3 in order to determine whether
detachment extends beyond the outer divertor nose as the density is raised. We
had a number of shots with density in the range 1.6e20<nebar<2.25e20/m3 in
order to 'probe' parameter space where the high-pressure region at the
divertor occurred. It disappears from the outer divertor for densities above
nebar >2e20/m3 (and below 1.6e20). There is also a pressure peak on the inner
divertor which may also be greater in magnitude than upstream. We have to
check further with the mapping to the FSP to verify this result.

On Wednesday we operated for the first time with the divertor on the flat
plate targets at the top of the machine. The objective of establishing a
well-controlled top-xpoint plasma was achieved without difficulty. This
satisfies Milestone #53 ("Initial Flat Plate Divertor Operation"),
approximately two months ahead of schedule. The uni-directional plume observed
when trace gases are injected from the capillary tubes on the inner midplane
was found to reverse direction when the x-point was moved to the top,
indicating that the flow is in fact toward the divertor in each case.
Quantitative measurements of this effect were obtained for different
ionization states of carbon (methane puff) and helium, as well as for D2
puffs.

Thursday and Friday's runs were devoted to RF systems checkout, following
cleanup and reconnection of the D-port coax. Balance detectors were added to
the two 6" loops and an optical arc detector was added to the bottom 4" coax
and feedthrough area. Because of reconfigurations to the transmission lines,
we had to recalibrate the electrical lengths. We have verified that the
balance detector works. By the end of the run on Friday, RF power in excess
of 1 MW was coupled through each of the antennas; all indications are that the
power handling capability is consistent with that obtained prior to the arcing
incident reported two weeks ago.

Dr. Garry McCracken participated in the TPX Divertor Diagnostics Meeting in
San Diego.

Dr. Earl Marmar participated in the meeting of the PBX-M Program Advisory
Committee at PPPL.