Kink Instabilities of a Toroidal Screw Pinch

Kink instabilities in a screw pinch with a circular cross-section are studied in a toroidal geometry for β p ∼ ε -1/2 and q ( a )∼1, where ε is an inverse aspect ratio and q ( a ) is a safety factor at a plasma surface r = a . The constant-pitch force-free field surrounding a main plasma improves MHD stability, compared with a high β tokamak. However, it is necessary to satisfy the Kruskal-Shafranov limit, in order to ensure stable discharges in the toroidal geometry.