Nonlinear Evolution of the Internal Kink in Tokamaks

In a tokamak, if the safety factor q becomes equal to unity in the plasma, the kinked plasma equilibrium which is accessible from the initial axisymmetric equilibrium through an internal-kink instability is itself unstable with respect to ballooning modes. This suggests a two-step mechanism for internal disruptions. First an internal-kink-type instability begins. Then the plasma pressure is released through the ballooning instability.