From: IRBY@CMOD.PFC.MIT.EDU
Date: Tue, 6 Jan 1998 9:06:47 -0500
Reply-To: IRBY@PSFC.MIT.EDU
Message-ID: <980106090647.3ee00442@CMOD.PFC.MIT.EDU>
Subject: Alcator C-Mod Weekly Highlights
Organization: MIT Plasma Fusion Center
Newsgroups: sci.physics.plasma

Alcator C-Mod Weekly Highlights
January 5, 1997


Alcator C-Mod will resume plasma operation on January 6 after
approximately 2 weekly of maintenance over the holiday period. Though
many people were on vacation during this time some important work was
done. A leak at the ECDC waveguide window that was keeping the vessel
in the mid to high 10-8 Torr range was repaired. Machine base pressures
are now back in the low 10-8 Torr range. Some discharge cleaning
in helium was begun over the weekend, and will continue today through
tomorrow morning. Water cooling lines to the DNB cryopumps have
been installed in the test last and are ready to be connected to the
cryopumps. The DNB duct work has been completed through the diagnostic
labs and up to the point where cell entry will occur.
On the last run before the holidays work continued on the
JET similarity program. Up to 2MW of RF power was coupled into these
JET shaped plasmas. However, these discharges produced
ELM-free H-modes which generally have more impurity accumulation. RF
coupling to these plasmas is also more difficult. The same shape at 1MA is
also ELM-free, whereas the normal, higher triangularity shape at 1MA are EDA.
This is strongly suggestive that it is the triangularity that controls the
EDA, although there are of course simultaneous changes in the divertor
strike-point geometry that also could have an effect.
We should have mentioned in an earlier report that Dr. Gerd Schilling,
Dr. Randy Wilson, and Dr. Joel Hosea of PPPL visited during the last full
week of plasma operation before the holidays as part the PPPL collaboration.
They participated in RF operations and analysis.
Ricky Maqueda from Los Alamos visited C-MOD during the week of 12/15.
The IR periscope was re-installed in C-MOD and the system became
operational on Thursday Dec. 18 (although not calibrated yet).
Preliminary results show that during non-disruptive discharges no substantial
wall heating is seen on the upper parts of the lower divertor noses, with the
exception of small "hot spots". This clearly changes during disruptions
that result in a downward movement of the plasma where heating of toroidal
bands and individual tiles is observed. The Los Alamos Fast Framing camera
was also operated during Ricky's visit. Using this camera the molybdenum
injections during RF heating can be clearly seen originating from the
upper edge of Bay E antenna.