A comment on magnetohydrodynamic stability of screw magnetic configuration in sharp boundary plasma

By using a model of sharp boundary plasma column surrounded by a vacuum, the magnetohydrodynamic stability in the screw magnetic field configuration has been investigated in detail for various of β, the ratio of plasma pressure to magnetic one. Relation between the growth rate of perturbation and β has also been studied. It is possible to find the completely stable configuration for under a certain critical value of β when the pitch length of magnetic field is smaller than the plasma radius and therefore the Kruskal-Shafranov limit does not exist. This fact arises from that a longitudinal trapped magnetic field and a conducting wall lead to very significant stabilizing effects on perturbations of kink mode as pointed out by R. J. Tayler. The maximum growth rates of perturbations become larger as the values of β increase. (auth.)