Nonlinear helical perturbations of the plasma in the Tokamak

Kink instability of a current-carrying highly conducting column in a strong magnetic field is considered in the general case without assuming the linear approximation. It is shown that helical penturbations should grow into bubbles'', i.e., plasma-free helical plaits which become inserted under the surface of the plasma column. The relation between this process and the so- called disruptive instability is discussed. (auth)