Stability of diffuse high-beta helical systems

The stability of m = 1 long-wavelength kink modes in diffuse high-β ℓ = 0 and ℓ = 1 systems has been investigated. For ℓ = 0 it is found that new modes exist with potentially dangerous growth rates and mode structure but which degenerate into zero growth-rate modes in the sharp boundary limit. The existence of such modes provides an explanation to an apparent paradox in the literature concerning ℓ = 0 wall stabilization. For ℓ = 1, it is found that the sharp boundary wall stabilization of the gross m = 1 mode remains essentially unchanged for diffuse profiles. This is favourable for the Scyllac programme.