First-Principles-Driven Model-Based Optimal Control of the Current Profile in NSTX-U
Z.O. Ilhan, W.P. Wehner, J.E. Barton, E. Schuster, D. Gates, S. Gerhardt, J. Menard
IEEE Multi-conference on Systems and Control
Sydney, Australia, September 21-23, 2015
Abstract
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Regulation in time of the toroidal current profile is one of the main
challenges toward the realization of the next-step operational goals
for the National Spherical Tokamak eXperiment - Upgrade (NSTX-U). In
this work, a nonlinear, control-oriented, physics-based model
describing the temporal evolution of the current profile is first
obtained by combining the magnetic diffusion equation with empirical
correlations obtained for the electron density, electron temperature,
and non-inductive current drives in NSTX-U. The proposed model is then
embedded into the control design process to synthesize a time-variant,
linear-quadratic-integral, optimal controller capa- ble of regulating
the safety factor profile around a desired target profile while
rejecting disturbances. Neutral beam injectors, electron density, and
the total plasma current are used as actuators to shape the current
profile. The effectiveness of the proposed controller in regulating
the safety factor profile in NSTX-U is demonstrated in closed-loop
nonlinear simulations.