Newsgroups: sci.physics.plasma
From IRBY@CMOD2.PFC.MIT.EDU Tue Jul 30 22:28:49 1996
From: IRBY@CMOD2.PFC.MIT.EDU
Organization: MIT
Subject: Alcator C-MOD Weekly Highlights

Alcator C-MOD Weekly Highlights
July 30, 1996

We continue to prepare for plasma operation. Electron cyclotron
discharge cleaning has now begun and will continue through early next
week. ECDC is used to remove impurities (O2, H2O, C, etc) from the vessel
wall while "loading" it with deuterium. The magnets have now
been cooled down to operational temperature (typically -165 C), and power
tests have begun. The alternator was successfully commissioned last week
and was used for the first time this week during the power tests. These
tests will continue for the next couple of days as each supply is carefully
checked for proper operation first under PLC control, and then under HYBRID
command. The alternator response to higher and higher loads will also
be carefully monitored.
Installation of the divertor cryopump diagnostics and control
system continues. Connections from the cryopump to the PLC are complete
and cabling needed to control the LN2 and LHe transfer lines is being
installed. Initial cooldown tests of the cryopump should be underway
by early next week.
We continue to prepare diagnostics for plasma operation.
The ECE beamline has been re-installed and a calibration is planned for
later this week. Alignment of the two-color-interferometer is progressing.
Several fiber runs were finished last week and will be used for control and
data acquisition of new diagnostics. Work on the new divertor RGA has begun.
Various components such as the vacuum system, magnetic shielding, and
support hardware for the RGA are either nearly designed or under construction.
University of Texas FRC personnel continued disassembly and packing of
the diagnostic neutral beam. Approximately half of the support units
(power supplies and power conditioning units) were removed from the FRC labs
by the shipper. A shipping date to MIT is being determined.
In response to a query from the ITER JCT (Perkins, Wesley, Ortolani),
we have begun a systematic study of the dependence of disruptivity
(i.e. # of disruptions per second of plasma operation) on several
plasma parameters. ITER is particularly interested in the dependence
on q95 and kappa. C-Mod's disruption database, with relatively quick access
to the basic plasma parameters of thousands of discharges, provides good
statistics, even with the very fine parameter resolution (delta q95=0.1)
requested by ITER. For the q95 study, we find that in the normal flattop
range (4 <= q95 <= 6), the disruption frequency reaches its lowest value of
about 0.35 disruptions per second of plasma operation. However, as q95
decreases below 3.2, the disruption frequency rises dramatically, but
monotonically.

A paper by collaborators and C-Mod personnel was recently accepted for
publication in Phys Rev A:

'Dielectronic Recombination and Excitation Autoionization Rate
Coefficients for Potassiumlike Mo23+ to Fluorinelike Mo33+',
K.B.Fournier, W.H.Goldstein, A.L.Osterheld, M.Cohen, M.Finkenthal,
M.J.May, J.L.Terry, M.A.Graf and J.E.Rice