TOROIDAL STABILITY BOUNDARIES FOR TEARING MODES IN TOKAMAKS

The linear stability boundaries for resistive and ideal external modes in circular cross section tokamaks are studied by means of toroidal m agnetohydrodynamical (MHD) computations. The resistive MHD prediction at zero pressure is clearly more unstable than experimental results. F or Lundquist numbers S = tau(r)/tau(A) of the order 10(7) or larger, t he resistive stability boundaries for moderate beta are rather close t o the ideal ones. These boundaries are in reasonable agreement with ex perimental results. The stabilizing effect of a conducting wall is stu died. At high S, the lower limit to the inductance tends to be set by resistive wall modes rather than by tearing modes. (C) 1996 American I nstitute of Physics.