Control of External Kink Modes Near the Ideal Wall Limit Using Kalman Filtering and Optimal Control Techniques

The first experimental demonstration of active feedback suppression of rotating external kink modes near the ideal wall limit in a tokamak using Kalman filtering to discriminate the n = 1 kink mode from background noise is presented [1]. The Kalman filter contains a model that captures the dynamics of a rotating, growing n = 1 kink mode. Suppression of the external kink mode is demonstrated using this Kalman filter over a broad range of phase angles between the sensed mode and applied control field, and performance is robust at noise levels that render simple proportional and derivative gain feedback ineffective. The demonstrated experimental utility of a such a Kalman filter in affecting the external kink motivates development of more complete physics model based filters and the incorporation of methods to optimize the control system gain used to stabilize the resistive wall kink mode. We also present new results that indicate that the use of such optimal control feedback with a model reduction based eigen-mode representation of a VALEN finite element model of resistive wall mode feedback leads to enhanced performance for the base-line ITER wall mode control system in comparison to traditional, classical control law based systems [2].