Viscous effects on plasmoid formation from nonlinear resistive tearing growth in a Harris sheet

TL;DR

This paper investigates how viscosity influences plasmoid formation during nonlinear resistive tearing in a Harris sheet using full MHD simulations, revealing two distinct viscous regimes affecting plasmoid size and development.

Contribution

It identifies and characterizes two viscous regimes that modulate plasmoid formation and saturation, providing new insights into viscosity's role in magnetic reconnection.

Findings

In low viscosity regimes, plasmoid width increases sharply with viscosity.

In viscosity-dominant regimes, plasmoid size decreases gradually with viscosity.

Viscosity significantly affects plasma flow and reconnection dynamics.

Abstract

In this study, the evolution of a highly unstable m = 1 resistive tearing mode, leading to plasmoid formation in a Harris sheet is studied in the framework of full MHD model using the NIMROD simulation. Following the initial nonlinear growth of the primary m = 1 island, the X-point develops into a secondary elongated current sheet that eventually breaks into plasmoids. Two distinctive viscous regimes are found for the plasmoid formation and saturation. In the low viscosity regime (i.e. P r . 1), the plasmoid width increases sharply with viscosity, whereas in the viscosity dominant regime (i.e. P r & 1 ), the plasmoid size gradually decreases with viscosity. Such a finding quantifies the role of viscosity in modulating the plasmoid formation process through its effects on the plasma flow and the reconnection itself.