MHD stability properties of a high current, high beta tokamak

Various aspects of MHD stability are studied for a high current, high beta tokamak. Included is a study of kink and ballooning mode beta limits as a function of current and safety factor at the plasma edge (q s ). These studies were carried out with pressure profiles optimized with respect to ballooning and ohmically consistent current profiles whereby the ⟨ ⋅ ⟩/⟨ ⋅∇ϕ⟩ profile is specified. The effect of current profile shaping is studied. Current profiles with steep edge gradients are more unstable to kink instabilities at high beta. This is particularly true for values of q s near an integer value on edge where the kink mode beta limit can fall off steeply. For a less steep edge current gradient, the ballooning modes are more unstable at high beta. The effect of elongation and triangularity are also considered. Improvement in the beta limit is observed for increasing elongation, up to κ = 2.0, after which beta drops off. A modest increase in triangularity does not improve the overall beta limits.