Effect of the curvature and the β parameter on the nonlinear dynamics of a drift tearing magnetic island
We present numerical simulation studies of 2D reduced MHD equations investigating the impact of the electronic βparameter and of curvature effects on the nonlinear evolution of drift tearing islands. We observe a bifurcation phenomenon that leads to an amplification of the pressure energy, the generation of E \times B poloidal flow and a nonlinear diamagnetic drift that affects the rotation of the magnetic island. These dynamical modifications arise due to quasilinear effects that generate a zonal flow at the onset point of the bifurcation. Our simulations show that the transition point is influenced by the βparameter such that the pressure gradient through a curvature effect strongly stabilizes the transition. Regarding the modified rotation of the island, a model for the frequency is derived in order to study its origin and the effect of the βparameter. It appears that after the transition, an E \times B poloidal flow as well as a nonlinear diamagnetic drift are generated due to an amplification of the stresses by pressure effects.