Active and passive stabilization of n  =  0 RWMs in future tokamak devices

The aim of this paper is to study the effects of the plasma aspect ratio, plasma elongation and plasma-wall distance on passive stabilization; this will be quantified by the plasma stability margin and instability growth time. Following this first step, the key aspects and figures of merit of plasma active vertical stabilization will be reviewed, with specific emphasis on the maximum disturbances that can be recovered by the plasma control system while minimizing active currents and voltages. Out of the (ex) vessel, optimally placed stabilization coils will be considered. The final goal being the study of the interplay among plasma elongation and the parameters described above to achieve robust passive and active stabilization. By fixing the maximum control voltage, the optimal position of the active coils is derived by estimating the maximum stabilizable vertical displacement and the envelope of current-power requirements for the active control system.