Control of resistive wall modes in tokamak plasmas

Tokamak control systems have to deal with different kinds of instabilities related to the presence of a resistive wall that surrounds the plasma. These instabilities are known as Resistive Wall Modes and are both axisymmetric and non-axisymmetric; they can occur during normal operation of the tokamak, and therefore suitable feedback controllers need to be designed and implemented. In this paper we propose a control architecture able to deal with the two main instabilities: the axisymmetric vertical instability and the non-axisymmetric kink instability. With reference to the case of the ITER tokamak, we design a controller consisting of two separate loops, one for the vertical stabilization and the other one for the stabilization of the kink instability. The two loops are designed in such a way to minimize the control effort and the interaction between them. The effectiveness of the approach is shown in simulation on an appropriate ITER configuration.