Control of Resistive Wall Mode Using a Matched Filter Eigenmode Approach
J. Blair, E. Schuster, D.A. Humphreys, Y. In, M.L. Walker and A. Welander
Division of Plasma Physics (DPP) Annual Meeting of the American Physical Society (APS)
Philadelphia, Pennsylvania, October 30-November 3, 2006
Abstract
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One of the major non-axisymmetric instabilities under study in the
DIII-D tokamak is the resistive wall mode (RWM), a form of plasma kink
instability whose growth rate is moderated by the influence of a
resistive wall. The Far-Tech RWM model represents the plasma surface
as a toroidal current sheet and represents the wall using an eigenmode
approach [1]. Although the plasma surface deformation cannot be
directly measured in real time, the magnitude and direction of the
deformation can be deduced from measurements by a set of 22 magnetic
field sensors and sad- dle loops. An array of 6 control coils can then
be used to return the plasma to its original shape. Using an estimator
for the two orthogonal components (related by quadrature in toroidal
angle) of the assumed n=1 mode, the resultant plant is reduced from a
22 by 6 system to a simple 2 by 2 system. Several control techniques
are considered to stabilize this system. The various approaches are
compared for their individual advantages and disadvantages.
Implications for experimental im- plementation and use are discussed.
[1] Y. In, et al, "Model-based dynamic resistive wall mode
identification and feedback control in the DIII-D tokamak," Phys. Pl.
13 (2006) 062512