Combined Rotation Profile and Plasma Stored Energy Control for the DIII-D Tokamak via MPC

W.P. Wehner, J.E. Barton, E. Schuster, M.L. Walker, D.A. Humphreys

American Control Conference

Seattle, WA, USA, May 24-26, 2017

Abstract

Tokamak plasma rotation is widely recognized for its importance to heat confinement and plasma stability. In this work we consider control of the plasma rotation profile with the aim of building a control strategy suitable for testing various rotation profiles for stability characteristics and reaching desired operating conditions. To obtain a control-oriented model of the toroidal rotation profile evolution, a simplified version of the momentum balance equation is combined with scenario-specific models for the momentum sources. Various momentum sources including on-axis and off-axis neutral beam injection and the non-axisymmetric field coils, which provide rotation damping, allow not only control of the bulk plasma rotation, but also control of the profile shape. A feedback controller is designed in a model predictive control framework to regulate the rotation profile while satisfying constraints associated with the desired plasma stored energy and beta (kinetic to magnetic pressure ratio) limits.