Simultaneous Optimal Regulation of Kinetic+Magnetic Scalar Plasma Properties for Robust Sustainment of Advanced Scenarios in NSTX-U

H. Al Khawaldeh, S.T. Paruchuri, Z. Wang, T. Rafiq, E. Schuster

29th IAEA Fusion Energy Conference

London, UK, October 16-21, 2023

Abstract

A control algorithm based on real time optimization has been developed for the simultaneous regulation of kinetic and magnetic scalar parameters in NSTX-U. This active control algorithm can contribute to operation optimization in tokamaks by regulating advanced scenarios characterized by steady-state operation, stable plasma confinement, and high-performance plasma. Actively shaping plasma profiles such as the safety factor is key in achieving and sustaining these advanced scenarios. However, as the number of control objectives to be addressed simultaneously increases, the profile-control problem may need to be reduced to the regulation of the profile at a few spatial locations due to controllability limits. In this case, the control objectives are reduced to a finite number of scalar plasma parameters, such as plasma-profile values at specific spatial points or volume-averaged plasma properties. On the positive side, effective simultaneous regulation of these scalar parameters may be all what is needed to achieve a desired scenario. A model-based optimal-control algorithm for simultaneous regulation of the central and boundary values of the safety-factor (q) profile, internal inductance (li), and normalized beta (βN ) has been developed in this work. The control algorithm has been designed based on control-oriented state models for the poloidal magnetic flux profile (ψ) and the plasma stored energy (W ) coupled with output models for q, li and βN . Moreover, in order to demonstrate robustness against model uncertainties, the proposed control algorithm has been tested in higher-fidelity, nonlinear simulations using COTSIM (Control Oriented Transport SIMulator).