A control scheme to deal with coil current saturation in a Tokamak

In this paper, we present a new approach for the design of a plasma current and shape feedback control system in a Tokamak. This approach takes explicitly into account the problem of current saturation in the coils which are used for the control action. The proposed design technique is essentially aimed at enlarging the operating envelope in which the Tokamak can operate without current saturation. The proposed controller structure consists of two feedback loops: one is a standard linear time-invariant (LTI) controller designed with the H-infinity technique, which operates in the absence of current saturation; the second gracefully degrades the system performance when the coil currents approach their saturation limits. Some stability considerations on the overall control system are given, and a case study is presented.