The Role of Uncertainty in the Design of a Control System for Magneto Hydro Dynamic Instabilities in a Tokamak

摘要

A tokamak is a magnetic confinement system designed for achieving the conditions for nuclear fusion reactions. The regime of stable operation in current and density in a tokamak is limited by disruptions which involve sudden loss of confinement. Density limit disruptions are connected with the evolution of Magneto Hydro Dynamics (MHD) instabilities associated to magnetic islands (tearing modes). Active control of MHD instabilities is important in order to improve tokamak performance. Localized heating by electron cyclotron heating systems (ECH) is a promising tool for an active control of the MHD behaviour of the discharge. The ECH heating system, composed by several high power ECH line sources that can be steered independently, must be controlled in order to deposit the heating power in a plasma layer as close as possible to the magnetic island position. In order to assure the fastest stabilization action of the feedback control system a new scheme has been proposed for the International Thermonuclear Reactor (ITER) that will be experimented in the next two years on the German tokamak ASDEX Upgrade. The novelty of the proposed control scheme is that the control action will make use explicitly not only on the estimate of the magnetic island and ECH heating plasma layer positions, but also on the uncertainties of these estimates.