Plasma vertical stabilization with actuation constraints in the DIII-D tokamak
E. Schuster, M.L. Walker, D.A. Humphreys and M. Krstic
Automatica, 41, pp. 1173-1179, 2005
Abstract
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In the Advanced Tokamak (AT) operating mode of the DIII-D tokamak, an integrated
multivariable controller takes into account highly coupled influences of plasma equilibrium
shape, profile, and stability control. Time-scale separation in the system allows a multiloop
design: the inner loop closed by the nominal vertical controller designed to control a
linear exponentially unstable plant and the outer loop closed by the nominal shape controller
designed to control a linear stabilized plant. Due to actuator constraints, the nominal vertical
controller fails to stabilize the vertical position of the plasma inside the tokamak when large or
fast disturbances are present or when the references coming from the shape controller change
suddenly. Anti-windup synthesis is proposed in this paper to find a nonlinear modification of
the nominal vertical controller that prevents vertical instability and undesirable oscillations
but leaves the inner loop unmodified when there is no input saturation.