A Two-time-scale Model-based Combined Magnetic and Kinetic Control System for Advanced Tokamak Scenarios on DIII-D
W. Shi, W. Wehner, J. Barton, M.D. Boyer, E. Schuster, D. Moreau, T.C. Luce, J.R. Ferron, M.L. Walker, D.A. Humphreys, B.G. Penaflor and R.D. Johnson
51th IEEE Conference on Decision and Control
Maui, Hawaii, December 10-13, 2012
Abstract
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System identification techniques have been successfully used to obtain
linear dynamic plasma response models around a particular equilibrium
in different tokamaks. This paper identifies a two-time-scale dynamic
model of the rotational transform iota profile and beta_N in response
to the electric field due to induction as well as to heating and
current drive (H&CD) systems based on experimental data from DIII-D.
The control goal is to regulate the plasma iota profile and beta_N
around a particular target value. A singular value decomposition (SVD)
of the plasma model at steady state is carried out to decouple the
system and identify the most relevant control channels. A mixed
sensitivity H_inf control design problem is solved to determine a
stabilizing feedback controller that minimizes the reference tracking
error and rejects external disturbances with minimal control energy.
The feedback controller is augmented with an anti-windup compensator,
which keeps the given controller well-behaved in the presence of
magnitude constraints in the actuators and leaves the nominal
closed-loop unmodified when no saturation is present. Experimental
results illustrate the performance of the proposed controller, which
is one of the first profile controllers integrating magnetic and
kinetic variables ever implemented in DIII-D.