Аннотация:Numerical methods are used to study the conditions under which the plasma column in a tokamak goes into a regime with a low value q/sub a/<2. The results of the linear theory for various current distributions are first discussed briefly. The nonlinear problem is then studied on the basis of reduced MHD equations with a finite conductivity for a low-..beta.. plasma. The vacuum region is described by a low conductivity. If the current has a profile with a significant peak, so that the condition q/sub 0/< or approx. =1 holds, the motion stabilizes after the nonlinear stage is passed. Localized currents near the surface which are caused by the plasma motion rapidly diffuse into the hot region. The subsequent evolution of the process is determined by the skin time of the hot part of the plasma column.