A magnetohydrodynamic stability study of reverse shear equilibria in the Tokamak Fusion Test Reactor

Abstract

A study is presented of the low‐n (n=1,2,3) magnetohydrodynamic stability of equilibria with reverse shear safety factor profiles. The low‐n stability boundaries are found to be characterized by resonance structures due to internal so‐called ‘‘infernal’’ mode types of instabilities. The parametric dependence of shear reversal width and depth, current, and pressure gradient on the beta limit are determined by using profile models that allow each parameter to be varied independently. Reverse magnetic shear is found to have a stabilizing influence for modes with toroidal mode numbers n≥2 leading to the possibility of improved β limits in the Tokamak Fusion Test Reactor (TFTR) [Plasma Phys. Controlled Nucl. Fusion Res. 26, 11 (1984)].