Helical core tokamak MHD equilibrium states

Bifurcated magnetohydrodynamic (MHD) tokamak equilibrium states with axisymmetric or helical core structure are computed. When a peaked pressure profile is chosen, the helical core structures appear like the snakes that are observed in the JET tokamak. They also have the allure of saturated ideal internal kinks. The existence of a magnetic island is not a requisite condition. Novel equilibrium states that can model the snake are obtained for a JET configuration when the q-profile has weak reversed magnetic shear with minimum q values in the range 0.94 to 1.03. At the lower end of this qmin range, the equilibrium snake structure lies radially well inside the domain for which qmin ≤ 1. Free boundary equilibria computed for the TCV tokamak develop helical cores when βN exceeds 0.3 and have a significant axis excursion for βN ≥ 0.4. At fixed (β) = 1.6%, the distortion of the magnetic axis is large in the range 0.95 ≤ qmin ≤ 1.01. The plasma–vacuum interface is not significantly altered by the internal helical deformations.