INDUCED SURFACE CURRENT EFFECTS OF A MAGNETIZED PLASMA

The linearized MHD perturbation theory of a magnetically confined plasma is reconsidered, with special emphasis on systems where there is a spatially inhomogeneous magnetic field part generated by constant currents in fixed externa] conductors. Electromagnetic induction then leads to induced surface current effects at the plasma boundary, due to the inhomogeneity of the externally imposed magnetic field. The corresponding surface currents are physically different from those which arise from the pressure balance condition at the plasma boundary. The apparent contradiction between the electromagnetically induced surface current effect and the pressure balance condition at the boundary is resolved by a transfer of the force due to the surface current into a volume force acting on the entire plasma body. The integrated effect of the surface current is thus included in the form of an additional volume contribution to the change in potential energy, whereas all other parts of conventional theory and its boundary conditions are preserved in the present approach. The induced surface current effect has often a stabilizing influence on the plasma displacements, as demonstrated by some concrete examples, including the behaviour of a plane kink disturbance in a Z-pinch with a superimposed octupole field.