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 explic itly into account the problem of current saturation in the coils which are used for the control action. The proposed design technique is essentially a imed at enlarging the operating envelope in which the Tokamak can operate w ithout current saturation. The proposed controller structure consists of tw o feedback loops: one is a standard linear time-invariant (LTI) controller designed with the H-infinity technique, which operates in the absence of cu rrent saturation; the second gracefully degrades the system performance whe n the coil currents approach their saturation limits. Some stability consid erations on the overall control system are given, and a case study is prese nted.