Physics-based Control-oriented Modeling of the Current Density Profile Evolution in NSTX-Upgrade
Z.O. Ilhan, J.E. Barton, E. Schuster, D.A. Gates, S.P. Gerhardt, J.E. Menard
Fusion Engineering and Design, 123 (2017) 564–568
Abstract
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Active control of the toroidal current density profile is among those
plasma control milestones that the National Spherical Torus
eXperiment-Upgrade (NSTX-U) program must achieve to realize its
next-step operational goals. Motivated by the coupled, nonlinear,
multivariable, distributed-parameter plasma dynamics, the first step
towards control design is the development of a physics-based,
control-oriented model for the current profile evolution in response
to non-inductive current drives and heating systems. The evolution of
the toroidal current density profile is closely related to the evolution
of the poloidal mag- netic flux profile, whose dynamics is modeled by
a nonlinear partial differential equation (PDE) referred to as the
magnetic-flux diffusion equation (MDE). The proposed control-oriented
model predicts the spatial-temporal evolution of the current density
profile by combining the nonlinear MDE with physics- based correlations
obtained at NSTX-U for the electron density, electron temperature, and
non-inductive current drives (neutral beams). The resulting
first-principles-driven, control-oriented model is tailored for NSTX-U
based on predictions by the time-dependent transport code TRANSP. Main
objectives and possible challenges associated with the use of the
developed model for the design of both feedforward and feedback
controllers are also discussed.