Newsgroups: sci.physics.plasma
From IRBY@CMOD2.PFC.MIT.EDU Tue Apr 30 16:06:32 1996
From: IRBY@CMOD2.PFC.MIT.EDU
Organization: MIT
Subject: Alcator C-MOD Weekly Highlights

Alcator C-MOD Weekly Highlights
April 30, 1996

The spring maintenance period continues with considerable progress
being made on RF systems, invessel divertor work, and diagnostic support
activities.
Sections of coax, RF switches, and directional couplers were among
the first set of components that arrived here from PPPL last week.
These components have been loaned to MIT by PPPL as part of
our RF collaboration. They will allow us to prepare well ahead of time
for the delivery of the final power amplifiers and tunable cavities in
July of this year (also from PPPL). We are very grateful for the well
organized way this transfer was handled by the PPPL staff. The FMIT
interconnecting cables were also included in the shipment, and
are being installed in the cable trays. Control testing of the FMIT
transmitters could be started as soon as this wiring is complete.
Transmitter #3 switchgear and its motorized disconnect have been tested
and are now operational. Transmitter #4 switchgear has been tested
and made operational. The motorized disconnect for #4 is now being
debugged. PLC crates are being installed in the new transmitter control
cabinets. All PLC cabling has been completed and is ready to be
installed. The primary cooling system wiring for both new transmitters
is now complete. Quotes are being requested for the plumbing required to
interface to the building de-ionized water system.
We continue to reassemble the alternator now that the inspection
is complete. All work on the water cooling lines has been completed.
The reconditioned flywheel bearings have been installed, as have the
rotor and rotor bearings. The drive motor is now being moved back into
position after which the system alignment can begin. The lift-pump high
pressure hoses have also been installed.
Invessel work consisted mainly of documentation of the outer
divertor in preparation for its removal. For example, the main support
bolts that secure the divertor to the vessel gussets have been checked
for torque and belleville washer stack compression. This information will
be used to help judge the performance of the current divertor design.
The rail system mounted to the upper gussets needed to transport the heavy
divertor modules within the vessel has been installed.
The TORVAC equipment rack has been moved to the west diagnostic
stand extension, and cabling is being relocated and extended where required.
Plans are now being made to relocate the diborane control cabinet to the
east stand extension. This change will create more room for the new edge
Thomson scattering experiment. Work continues on the East wall extension.
The grating, matting, and kick plates remain to be installed. Fiber
optic cable runs are being installed for new diagnostics.
Analysis of data from the last experimental campaign continues.
Previously, a clear threshold for the L-H transition was found in
the edge temperature (measured at the 95% flux surface). Recent analysis
of discharges from the last run period has shown that the quality of the
confinement in fully developed H modes are correlated with the edge
temperature as well. Perhaps more importantly, the temperature gradient
in the plasma core is found to depend clearly on the edge temperature.
For example, the edge temperature is lowered by ELMs and these
discharges show lower core temperature gradients compared to ELM free
plasmas at the same density and input power. This result may suggest a
marginal stability model where the temperature at the top of the
transport barrier sets the gradient and temperature profile in the
plasma interior.
Preliminary bolometric results indicate that a significant fraction
of the measured radiated power from the main plasma is due to escaping
neutrals. Also, it has been observed that the neutral contribution
decreases substantially during ELM free H-modes. Work is in progress
to analyze the contributions from various factors, and to explore the role
of neutrals in H modes.
Yuichi Takase was at the FEAC Alternate Concepts Panel meeting
in Chicago last week. A. Pigarov from PPPL gave the Fusion Center seminar
on Recent Developments in Atomic-Molecular Process for Divertor Plasmas.