Non-circular tokamak plasmas can be unstable to ideal-MHD axisymmetric instabilities. Passive conductors with finite resistivity will at best slow down these instabilities to the resistive (L/R) time of the conductors. It is demonstrated that a simple active feedback system far from the plasma which responds on this resistive time can stabilize the system, provided its mutual inductance with the passive coils is small enough.
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Jardin et al. (1982) studied this question.