Current Profile Tracking for the DIII-D Tokamak via LQI Optimal Control
M.D. Boyer, J. Barton, E. Schuster, M.L. Walker, T.C. Luce, J.R. Ferron, B.G. Penaflor, R.D. Johnson and D.A. Humphreys
51th IEEE Conference on Decision and Control
Maui, Hawaii, December 10-13, 2012
Abstract
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In tokamak fusion plasmas, controlling the spatial distribution
profile of the toroidal current is key to achieving advanced scenarios
characterized by confinement improvement and possible steady-state
operation. The dynamics of the current profile are nonlinear and
coupled with other plasma parameters, motivating the use of
model-based control strategies. In this work, we use a
control-oriented model of the current profile evolution in DIII-D to
design a feedback controller for regulating the profile arround a
desired trajectory. Without feedback, the response of the current
profile to disturbances, model uncertainty, and perturbed initial
conditions can be undesirable. To improve tracking performance of the
system, a nonlinear input transformation is combined with a
linear-quadratic-integral (LQI) optimal controller designed to
minimize a weighted combination of the tracking error and controller
effort. The resulting control law utilizes the total plasma current,
total external heating power, and line averaged plasma density as
actuators. We present simulation and experimental results showing
successful rejection of perturbed initial conditions and input
disturbances.