Stability properties of a toroidal z-pinch in an external magnetic multipole field

MHD stability of m = 1, axisymmetric, external modes of a toroidal z-pinch immersed in an external multipole field (Extrap configuration) is studied. The description includes the effects of a weak toroidicity, a non-circular plasma cross-section and the influence of induced currents in the external conductors. It is found that the non-circularity of the plasma cross-section always has a destabilizing effect but that the m = 1 mode can be stabilized by the external feedback if the non-circularity is small. (orig.)