Non-linear helical MHD instability

The development of MHD instability with time in a plasma cylinder is considered. It is shown that the development of instability is resonant in character. When maximum instability is achieved at the non-linear stage, the instability embraces the whole of the plasma cross-section and causes the magnetic surfaces to be turned inside out. In a toroidal geometry the instability considered is evidently stabilized by a magnetic well with certain limitations on the current distribution in the plasma.