Newsgroups: sci.physics.plasma
From IRBY@CMOD2.PFC.MIT.EDU Tue May 14 17:41:27 1996
From: IRBY@CMOD2.PFC.MIT.EDU
Organization: MIT
Subject: Alcator C-MOD Weekly Highlights

Alcator C-MOD Weekly Highlights
May 14, 1996

The spring maintenance period continues. The outer divertor,
RF systems, divertor cryopump, and edge Thomson scattering are
making good progress.
All outer divertor modules have been removed from the vessel
and machining and welding of the components have begun. As described in
more detail last week, changes to the outer divertor module are being made
to increase the shear strength of the outer divertor mother bolts. These
bolts provide the major points of attachment for the outer divertor module
to the vacuum vessel wall. Ultrasonic testing of the outer divertor
tiles has also begun.
The divertor cryopump has been put through several complete cooldown
cycles, and the PLC/PC hardware and software debugged. The new cryogenic
valves for controlling LN2 and LHe to the pump have arrived and are being
checked out and readied for installation.
The control cabinets for the new RF transmitters have been moved
from our setup area to their final location in the power room. The
control wiring can now continue. Two new 9" coax runs from the
new transmitters have been layed out and support hardware is now
being determined. The new switchgear units have been successfully
operated remotely and can now be wired to the PLC.
Joe Bartolick from PPPL was here last week installing components
for the new Edge Thomson Scattering system. The laser table, and beam
handling optics are installed. The laser power and cooling water have been
hooked up, and the flashlamps made operational. The optics mounted to the
igloo are installed except for the final turning mirror which
is awaiting welding to the A-port cowl. The HeNe alignment beam
has been successfully directed down the entire optical path up to
the last mirror position. The polychromator and electronics rack are in
position in the cell and cabling is being installed. Preparations are being
made for test firing the laser to determine if there is any electrical noise
detectable in the ECE system. The laser and the ECE detector electronics
occupy the same diagnostic lab.
The diborane gas cabinet has been wired up at its new location,
and preparations are being made to relocate the associated vent lines.
Analysis of data from the last run continues. Large up-down
asymmetries in Ar16+ x-ray brightnesses have been observed from the edge
of Alcator C-Mod plasmas. Modelling of the observed brightness profiles
indicates that the brightness asymmetries can be explained by an asymmetry in
the Ar17+ density of a factor of 8, just inside the last closed flux surface.
This asymmetry is in the opposite direction from the ion B X grad B drift
direction, and is in qualitative agreement with the predictions of
neo-classical parallel impurity transport theory.
Two of our collaborators, Kevin Fournier (at LLNL and JHU) and Mark
May (at JHU) have performed a new calculation of the "cooling rate" of
molybdenum. The calculations use the latest atomic physics data and indicate
that in the 300-800 eV temperature range the emissivity per Mo ion per
electron is significantly higher than that of Post, Jensen, et al.
(Atomic Data and Nucl. Tables, Vol. 20 (1977). We plan to compare the
new predicted emissivities with profiles measured by bolometry.
Jim Irby attended the ITER Progress Meeting on Microwave
Diagnostics and the first Reflectometry Working Group meeting, both held
at the San Diego Joint Work Site. Ian Hutchinson and Miklos Porkolab
were at PPPL last week at an ITER Information Workshop.

Paper recently published or accepted for publication include:

J A Snipes, A E Hubbard, D T Garnier, S N Golovato, R S Granetz, M Greenwald,
I H Hutchinson, J Irby, B LaBombard, E S Marmar, A Niemczewski, P J O'Shea,
M Porkolab, P Stek, Y Takase, J L Terry, R Watterson, S M Wolfe, "H-modes on
Alcator C-Mod", to be published in Plasma Physics and Controlled Fusion,
approximately June 1996.

J. A. Snipes, R. L. Boivin, C. Christensen, C. Fiore, D. Garnier, J. Goetz,
S. N. Golovato, M. Graf, R. S. Granetz, M. Greenwald, A. Hubbard, I. H.
Hutchinson, J. Irby, B. LaBombard, E. S. Marmar, A. Niemczewski, P. O'Shea,
M. Porkolab, P. Stek, Y. Takase, J. L. Terry, M. Umansky, S. M. Wolfe,
Physics of Plasmas, Vol. 3 (1996) 1992.