Robust control of resistive wall modes in tokamaks

Active feedback stabilization of high-β tokamaks is studied using a new, rigorous construction of the transfer functions, based on an expansion in the resistive wall eigenmodes of the unstabilized, toroidal equilibrium. It is shown that a simple control system using poloidal sensors can give robust stabilization for equilibria within a wide range of plasma currents and rotation speeds. The required coil voltages are modest, even for the two-wall structure of ITER.