Viscous effects on nonlinear double tearing mode and plasmoid formation in adjacent Harris sheets

TL;DR

This study investigates how viscosity influences the nonlinear evolution of double tearing modes and plasmoid formation in adjacent Harris sheets, revealing a critical Prandtl number that determines plasmoid types and flow behavior.

Contribution

It provides new insights into the viscous effects on double tearing mode dynamics and plasmoid formation, highlighting the role of the Prandtl number in these processes.

Findings

Normal and monster plasmoids are generated at Pr = 1.

Generation of monster plasmoid is halted when Pr exceeds a critical value.

Flow advection patterns depend on the Prandtl number regime.

Abstract

In this paper, we study the effects of viscosity on the evolution of double tearing mode (DTM) in a pair of adjacent Harris sheets based on the resistive MHD model in the NIMROD code. Similar to the tearing mode in the conventional single Harris sheet, a transition is observed in the generation of both normal and monster plasmoids at Pr = 1. In the Pr < 1 regime of DTM, normal plasmoids (small plasmoids) are generated along with monster plasmoid, whereas in the single tearing mode (STM) cases such a generation is not observed. When Pr is above the critical value, the generation of monster plasmoid is halted. Correspondingly, in the Pr < 1 regime, a quadrupolar flow advects along poloidal direction, but in Pr > 1 regime this flow advection is inhibited.