Plasma rotation effects on the trigger and the evolution of MHD activities in reversed shear profiles are studied by nonlinear MHD simulations. It is found that, in a rotating plasma, magnetic islands formed around the inner and outer magnetic resonant surfaces, which are stable for the tearing mode, by an external perturbation (driven magnetic island), evolve with different growth rates during an initial growth phase. After the initial growth phase, an outer magnetic island grows rapidly prior to the inner one and triggers a rapid growth of the inner magnetic island. At the final phase, enlarged magnetic islands flatten a q-profile in a wide radial region including the plasma centre. Though this final phase closely resembles a nonlinear destabilization of a spontaneous double tearing mode (Ishii et al 2002 Phys. Rev. Lett.89 205002), this process can explain the time delay of a plasma edge oscillation in triggering an internal MHD event and disruption.
Radial electric field and transport near the rational surface and the magnetic island in LHD