Performance Assessment of Model-Based Optimal Feedforward and Feedback Current Profile Control in NSTX-U using the TRANSP Code
Z. Ilhan, W.P. Wehner, E. Schuster, D. Boyer, D. Gates, S. Gerhardt and J. Menard
Division of Plasma Physics (DPP) Annual Meeting of the American Physical Society (APS)
Savannah, GA, USA, November 16-20, 2015
Abstract
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Active control of the toroidal current density profile is crucial to
achieve and maintain high-performance, MHD-stable plasma operation in
NSTX-U. A first-principles-driven, control-oriented model describing
the temporal evolution of the current profile has been proposed earlier
by combining the magnetic diffusion equation with empirical correlations
obtained at NSTX-U for the electron density, electron temperature, and
non-inductive current drives. A feedforward + feedback control scheme
for the regulation of the current profile is constructed by embedding
the proposed nonlinear, physics-based model into the control design
process. Firstly, nonlinear optimization techniques are used to design
feedforward actuator trajectories that steer the plasma to a desired
operating state with the objective of supporting the traditional
trial-and-error experimental process of advanced scenario planning.
Secondly, a feedback control algorithm to track a desired current
profile evolution is developed with the goal of adding robustness to
the overall control scheme. The effectiveness of the combined
feedforward + feedback control algorithm for current profile regulation
is tested in predictive simulations carried out in TRANSP.