To the analytical theory of internal screw modes

The internal screw modes in a tokamak are studied theoretically. It has been shown that the equation for perturbations in the ideal area has an exact analytical solution in terms of hypergeometrical functions in the case of the parabolic distribution of longitudinal current and the analogous model profile of plasma pressure. The toroidal effects on the tearing modes were investigated. It has been shown that such modes could be stabilized at a finite aspect ratio. The ideal instabilities appearing at a sufficiently small shear were studied too. 30 refs.; 3 figs