Viscous Effects on Nonlinear Double Tearing Mode and Plasmoid Formation in Adjacent Harris Sheets

In this paper, we study the effects of viscosity on the evolution of the 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 Prandtl number P-r=1. In the P-r<1 regime of the 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 P-r is above the critical value, the generation of monster plasmoid is halted. Correspondingly, in the P-r<1 regime, a quadrupolar flow advects along the poloidal direction, but in the Pr>1 regime this flow advection is inhibited.