Nonlinear behaviour of collisionless double tearing mode induced by electron inertia

Abstract

A gyrokinetic particle simulation is executed to clarify the effect of the electron inertia on the MHD phenomena in the reversed shear configuration of a cylindrical tokamak plasma. It is found that the collisionless (kinetic) double tearing modes grow at the Alfvén time scale and nonlinearly induce the internal collapse when the helical flux at the magnetic axis is less than that at the outer resonant surface. After the internal collapse, the secondary reconnection is induced by the current concentration due to the m = 2 convective flow. It is also clarified that a nonlinear dynamics accompanying the elementary processes caused by the m = 2 flow can generate a new reversed shear configuration with resonant surfaces. In the presence of the density gradient, after the full reconnection induced by the m = 2 mode, the radial electric field is found to be generated due to the difference of the E × B motion between ions and electrons. However, the intensity of the radial field is not as large as that induced by the collisionless kink mode.