Optimum equilibria for high performance, steady state tokamaks

The dependence of the ideal ballooning beta limit on aspect ratio, A, and elongation kappa is systematically explored for nearly 100% bootstrap current driven tokamak equilibria in a wide range of the shape parameters (A = 1.2-7.0, kappa = 1.5-6.0 with triangularity delta = 0.5). The critical beta(N) is shown to be optimal at kappa = 3.0-4.0 for all A studied and increases as A decreases with a dependence close to A(-0.5). The results obtained can be used as a theoretical basis for the choice of optimum aspect ratio and elongation equilibria for future high performance steady-state tokamaks.