Nonlinear Physics-model-based Actuator Trajectory Optimization for Advanced Scenario Planning in the DIII-D Tokamak
J. Barton, W. Shi, E. Schuster, T.C. Luce, J.R. Ferron, M.L. Walker, D.A. Humphreys, F. Turco, R.D. Johnson and B.G. Penaflor
19th IFAC World Congress
Cape Town, South Africa, August 24-29, 2014
Abstract
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Extensive research has been conducted to find operating scenarios that
optimize the plasma performance in nuclear fusion tokamak devices with
the goal of enabling the success of the ITER project. The development,
or planning, of these advanced scenarios is traditionally investigated
experimentally by modifying the tokamaks actuator trajectories, such
as the auxiliary heating/current-drive (H&CD) scheme, and analyzing
the resulting plasma evolution. In this work, a numerical optimization
algorithm is developed to complement the experimental effort of
advanced scenario planning in the DIII-D tokamak. Two properties
related to the plasma stability and performance are the safety factor
profile (q-profile) and the normalized plasma beta. The optimization
algorithm goal is to design actuator trajectories that steer the
plasma to a target q-profile and normalized plasma beta, such that the
achieved state is stationary in time, subject to the plasma dynamics
(described by a physics-based, nonlinear, control-oriented partial
differential equation model) and practical plasma state and actuator
constraints, such as the maximum available amount of H&CD power. This
defines a nonlinear, constrained optimization problem that we solve by
employing sequential quadratic programming. The optimized trajectories
are then tested through simulation with the physics-based model and
experimentally in DIII-D.