NUMERICAL STUDY OF THE AXISYMMETRICAL IDEAL MHD STABILITY OF EXTRAP

A numerical study of the free-boundary axisymmetric (n = 0) ideal magn etohydrodynamical (MHD) motions of the EXTRAP device is presented. The dependence of stability on current profiles in the plasma and current s in the external conductors is investigated. Results are shown for li near growth-rates and nonlinear saturation amplitudes and their depend ence on plasma radius as well as on the conducting shell radius. The i nterior region of the plasma is simulated by means of a Lagrangian Fin ite Element Method (FEM) for ideal magnetohydrodynamics. The method is based on a nonlinear variational principle for the Lagrangian descrip tion of ideal MHD. The Boundary Element Method (BEM) is used together with the Lagrangian FEM to simulate nonlinear motion of an ideal MHD p lasma behaviour in a vacuum region under the influence of external mag netic fields.