Oscillation dynamics of m/n= 3/1 double tearing mode

Abstract

This study systematically investigates the roles of the plasma viscosity and resistivity in the oscillation dynamics during the decay phase of the m/n = 3/1 double tearing mode using the Ci-Liu-Ti (CLT) code. The primary objectives of this research are to examine the driving and suppressing mechanisms of the oscillation. The oscillation and steady-state are the result of the competition between the external injection and the reconnection annihilation of magnetic flux during the decay phase. In a regime with a higher viscosity (or a lower resistivity), the steady-state arises from the significant damping (weak generation) of plasma flows, resulting in the formation of saturated islands. In a regime with a lower viscosity (or a higher resistivity), the suppression of the oscillation amplitude can be attributed to a strong residual flow that quickly takes the injected magnetic flux away toward to the reconnection region, which caused no enough accumulated magnetic flux to drive oscillations and the system evolves toward a steady-state configuration. The steady-state condition results in the generation of a narrow radial vortex region which promotes formation of internal transport barriers. The upper threshold of the resistivity within the low-resistivity regime to achieve a steady-state decreases as the viscosity increases.