Newsgroups: sci.physics.plasma
From: FAIRFAX@CMOD2.PFC.MIT.EDU
Subject: Alcator Highlights, Aug. 4 & 11

Alcator C-MOD Weekly Highlights
August 4, 1994

The maintenance/repair period is continuing. Work on the new design for the
coax buss is proceeding. Prototype components incorporating the new design,
which features a more compliant head piece for the inner coax, have been
fabricated and will be tested. Additional calculations to verify the design
are in progress.

While the bus work proceeds, additional maintenance activities are also being
carried out. The vessel heaters, which are normally inaccessible, are
undergoing a thorough inspection.

In-vessel work this week has included removal of a set of tile modules on the
inner wall, in preparation for installation of new halo current diagnostics.
In addition, we will replace a few of the tiles with specially prepared
"tracer" tiles, containing a thin coating of tungsten under an overcoating of
molybdenum. This work, being carried out in collaboration with Sandia, will
investigate the erosion and re-deposition of molybdenum during high-power
operation.

A shot from the June, 1994, run period has been selected for additional
analysis using the DEGAS code; this work is being carried out by Daren Stotler
of PPPL. The particular shot,940623028, was part of a divertor studies run,
and includes density and temperature profiles at the target plate and
fast-scanning probe profiles in the main chamber, as well as a complete set of
H-alpha data. This shot was a low density discharge on which divertor
detachment did not occur.

C.H. Ma of ORNL is working at MIT this week, preparing his Faraday rotation
diagnostic. This diagnostic works in conjunction with our existing Two-Color
Interferometer (TCI), and will be used to measure the current density profile.
All of the main components of the rotation experiment are now installed on the
laser table, and rotations of the order of 2 degrees have been successfully
detected using a polarization rotator installed on the table.

Professor Ian Hutchinson has returned from his sabbatical at JET. Martin
Greenwald is participating in the ESNET Steering Committee Meeting in New
Mexico.
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Alcator C-MOD Weekly Highlights
August 11, 1994

The maintenance/repair period is continuing. Fabrication drawings for a
full-scale prototype of the new design for the inner coax conductor have been
approved and released to the vendors. Rough cut parts for the prototype coax
have already been produced.

Cleanup and resurfacing of the terminal plate for the OH2L coil has been
completed. All three coils in the OH stack have been electrically tested
(rung) at 600 volts.

All 400 vessel heaters have been checked out and are working correctly.

TRANSP is now being run in "production" mode. Analyses of about a dozen shots
from the 1993 and 1994 operating campaigns have been produced, with ten more
in progress. So far the analysis is being carried out for ohmic discharges.
Analysis of ICRF heating shots, using the TRANSP ICRF package, will begin
shortly.

In the course of attempting to resolve a small discrepancy (at the level of a
few percent) in our magnetic analysis, we have determined that the vacuum
vessel exhibits a small magnetic permeability. Our control system and
equilibrium analysis appear to be robust against this effect, as expected since
these depend principally on measurements of the fields and fluxes in vacuum
inside the vessel. The discrepancy shows up primarily when the vessel currents
inferred from the analysis are compared to those expected, or equivalently
when magnetics signals are compared with expected values based on integrating
the circuit equations using measured coil currents.

Dr. Roger Richards from ORNL is back at MIT this week, continuing
installation work for his laser scattering experiment.