Full-torus MHD equilibrium study of a low-shear helical-axis heliotron

摘要

The magnetohydrodynamic equilibrium of a helical-axis heliotron with large-vacuum magnetic islands is investigated. Since the helical-axis heliotron is an L = 1/M = 4 low-magnetic-shear configuration, there is the sensitivity to the perturbed field. By assuming the external trim coil, low-order magnetic islands with n/m = 1/2 can be generated. The effect and change of low-order (n/m = 1/2) vacuum islands to the finite beta equilibrium are investigated. For a finite beta equilibrium, n/m = 1/2 islands disappear but n/m = 4/8 islands appear by the pressure-induced field. For another case, n/m = 1/2 islands disappear and other resonances are suppressed. This property depends on the phase of islands.