Model-based Safety-Factor-Profile Slope Control at Predefined Rational Surfaces in DIII-D

Abstract

Magnetohydrodynamic instabilities like neoclassical tearing modes appearing at rational safety-factor surfaces can degrade and even disrupt plasma confinement. It has been proposed that active regulation of the safety-factor-profile slope at these rational surfaces may mitigate the onset of such instabilities [1]. Recently proposed algorithms for local control of the safety-factor profile rely on indirectly regulating the slope of the poloidal-flux-gradient profile to achieve the desired control objective [2]. However, due to the nonlinear relation between the safety factor and the gradient of the poloidal flux, regulating only the slope of the poloidal-flux-gradient profile may not always achieve the desired safety-factor-profile slope. A novel algorithm is proposed in this work based on a model that governs the evolution of the safety-factor-profile gradient, which enables control synthesis for direct regulation of the safety-factor-profile slope. The effectiveness of the proposed model and the associated model-based controller are demonstrated using nonlinear COTSIM simulations for a DIII‑D scenario. [1] K. Kim et al., APS Division of Plasma Physics Meeting 2018 (NP11.119). [2] S.T. Paruchuri et al., APS Division of Plasma Physics Meeting 2021 (GP11.013).

Sai Tej Paruchuri

Postdoctoral Research Associate in Plasma Control

My research interests include plasma control, dynamics and controls, vibrations and adaptive structures, data-driven modeling.