Description of the Plasma Potential Control (PPC) System on the Tandem Mirror Experiment-Upgrade (TMX-U) Page: 2 of 5
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A DESCRIPTION OF THE PLASMA POTENTIAL CONTROL (PPC) SYSTEM
ON THE TANDEM MIRROR EXPERIMENT-UPGRADE (TMX-U)
P. S. Surrena and R. H. Underwood
Lawrence Livermore National Laboratory
P. 0. Box 808, L-540
Livermore, CA 94550Abstract
A set of 18 separately controlled plates have been
added to each end of the Tandem Mirror Experiment
Upgrade (TMX-U) vessel to allow measurement of
end-wall currents and to provide a means of plasma
potential control (PPC). These plates are shaped to
form elliptical rings separated into quadrants. Each
plate can be individually grounded, float at plasma
potentials, or be actively biased to control the
plasma. Voltage and current monitoring are provided
for each of the plates, and the control and monitoring
functions are controlled by the PPC system computer.
The details of the field line mapping and the plate
shapes are discussed, and the control architecture and
performance are presented.
"Work performed under the auspices of the U.S.
Department of Energy by the Lawrence Livermore
National Laboratory under contract
number W-7405-ENG-48."
Introduction
Results from the Tandem Mirror Experiment-Upgrade
(TMX-U) demonstrate that radial transport in the
plasma volume can be affected by the electrical and
mechanical conditions at the end walls of the vessel
[1]. Transport reduction is necessary for longer
tandem-mirror confinement times. Experiments on the
TMX-U at Lawrence Livermore National Laboratory have
produced results that substantiate modifying end-wall
boundary conditions using floating. ring-shapedUCRL--92513
DE86 005142plates. This gave rise to the Plasma Potential
Control (PPC) System which provided a means to further
measure this phenomena. These measurements (in which
the end-wall plates, mapping to the plasma core, are
switched from a floating to a grounded condition
during plugging operation) demonstrate that this
floating increases the build-up rate of the central
cell plasma, steepens the core density profile, and
affect the plasma throughout the entire cross section.
To obtain these experimental results, the plates need
to have a mechanism to change their electrical status
during a typical 100 millisecond shot of ThX-U. Three
electrical states with respect to the TEX-U vessel,
grounded, floating and some bias potential, further
complicate the ! stallation of the equipment. To
obtain data on the effects the plates have on
confinement, each plate needs to have the ability to
change electrical states (possibly several times)
during the course of the shot. This mandated the use
of a computer stem and control architecture to
provide the required ,recision timing. This paper
discusses the PPC system and the performance levels
achieved.
Plate Requirements
For the Initial Installation of PPC in the TMX-U, t
plates cover about 80 percent of the total area in
each end wall. The end walls are rotated 900 from
each other so the elliptical plates are also rotated,
which conforms to the Tandem Magnetic Mirror
configuration of TMX-U (see Fig. 1).East plates looking east
1.
82
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Nam 83 E3 es mE I E]1 me 9I1 em ftm
ED6
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gemWest plates looking west
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-1-
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Surrena, P.S. & Underwood, R.H. Description of the Plasma Potential Control (PPC) System on the Tandem Mirror Experiment-Upgrade (TMX-U), article, November 11, 1985; California. (https://digital.library.unt.edu/ark:/67531/metadc1205009/m1/2/: accessed June 1, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.