RELATION OF VERTICAL STABILITY AND ASPECT RATIO IN TOKAMAKS

It is evaluated how the upper limit to plasma elongation kappa, caused by vertical stability, varies with the aspect ratio A = R/a of the tokamak. Equilibria were generated with EFITD and the vertical stability was assessed by GATO. For a 'generic' tokamak with a superconducting wall conformal to the plasma shape and a distance 0.5 a away from the plasma edge and a constant current profile (q0 = 1.0, l(i) congruent-to 1.0, q95 = 3.2) it is found that the maximum stable kappa decreased only slowly from 2.65 at A = 2.0 to 2.4 at A = 6.0. To first order, a reasonable assumption in trade-off studies of new machine designs is no dependence of kappa(max) on A.