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

S.T. Paruchuri, E. Schuster

Division of Plasma Physics (DPP) Annual Meeting of the American Physical Society (APS)

Spokane, WA, USA, October 17-21, 2022

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).

*Supported by the US DOE (DE-SC0010661, DE-FC02-04ER54698).