Evolutions of the local pressure gradient and the amplitude of the global resistive interchange instability are studied in torsatron/heliotron plasmas. (Torsatron/heliotron: the high-aspect-ratio toroidal helical plasma with magnetic shear and magnetic hill.) Coupled equations for the background pressure profile and a single helical mode are derived by keeping the effects of the thermal transport and ion viscosity. Three characteristic dynamic evolutions are identified; monotonic saturation relaxation oscillation and periodic limit cycle solution. As the heating power is increased, the dynamic evolution changes from monotonic saturation, to relaxation oscillation and finally to the limit cycle. The time average of the pressure gradient is limited by the critical gradient against the linear stability. Dependences of the amplitude and period of the sawtooth oscillation on the heating power are also analysed.
Stability of plasma cylinder in a time-dependent magnetic fleld