Model-based Linear-Quadratic-Integral Controller for Simultaneous Regulation of the Current Profile and Normalized Beta in NSTX-U
H. Al Khawaldeh, B. Leard, S.T. Paruchuri, T. Rafiq and E. Schuster
Symposium on Fusion Technology (SOFT)
September 18-23, Dubrovnik, Croatia, 2022
Achieving advanced scenarios that are characterized by steady-state
operation, stable plasma confinement, and high-performance plasmas is
one of the primary objectives of National Spherical Tokamak
eXperiment - Upgrade (NSTX-U). Active control of important plasma profiles
and scalars may be necessary to achieve these objectives. In particular,
control algorithms that can optimize the tokamak performance to achieve
the desired plasma profiles in any given scenario may be necessary. In
this work, a model-based optimal control algorithm is developed for
feedback control of the current profile in NSTX-U. The linear finite-dimensional
control model is derived by discretizing and linearizing the magnetic
diffusion equation in combination with empirical correlations used for
electron density, electron temperature, and noninductive current drives.
The linear time-variant model is then used for designing a
linear-quadratic-integral (LQI) controller that is capable of regulating
both the safety factor and the normalized beta around desired targets.
The controller determines neutral beam injector powers and the overall
plasma current to achieve the desired current profile and normalized beta.
The proposed controller is tested in higher-fidelity nonlinear simulations
that employ 1D models for both current and temperature profiles using the
Control Oriented Transport SIMulator (COTSIM). The closed-loop simulations
show the effectiveness of the controller at shaping the safety factor in
NSTX-U while achieving the desired normalized beta.
*Supported by the US DOE under DE-SC0021385.