Effect of the curvature and the {\beta} parameter on the nonlinear dynamics of a drift tearing magnetic island

TL;DR

This study uses numerical simulations to explore how the electronic eta parameter and curvature influence the nonlinear behavior of drift tearing magnetic islands, revealing bifurcations, flow generation, and stabilization effects.

Contribution

It introduces a detailed analysis of the nonlinear evolution of drift tearing islands considering eta and curvature effects, highlighting bifurcation phenomena and flow dynamics.

Findings

Bifurcation leads to pressure energy amplification and flow generation.

Pressure gradient and curvature effects influence transition stability.

Post-transition, flows and drifts are amplified by pressure effects.

Abstract

We present numerical simulation studies of 2D reduced MHD equations investigating the impact of the electronic \beta parameter 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 \beta parameter 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 \beta parameter. 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.