Plasmoid-dominated Turbulent Reconnection in a Low-beta Plasma

Abstract:

In magnetohydrodynamics (MHD), magnetic reconnection has been traditionally discussed by Sweet--Parker and Petschek models. Recently, it was found that a laminar Sweet--Parker reconnection evolves to plasmoid-dominated turbulent reconnection in a large-scale system. The reconnection rate during the plasmoid-dominated stage is known to be 0.01, regardless of other parameters.

Plasma beta in the inflow region is a key parameter in the reconnection system. It is extremely low around reconnection sites in a solar corona. However, despite its importance in a corona, many aspects of the plasmoid-dominated reconnection in the low-beta regime remain unexplored, partly because of numerical difficulties.

In this contribution, we explore basic properties of plasmoid-dominated reconnection in a low-beta background plasma, by using a highly-scalable MHD code [1]. We have found that the system becomes highly complex due to repeated formation of plasmoids and shocks. We have also found that the average reconnection rate increases in the beta < 1 regime, in contrast to popular results. We attribute this to compressible effects. Using a compressible reconnection theory, we have derived a scaling law. This prediction is verified by extensive numerical survey [2]. We will further explore the influence of the initial plasma-sheet models, and then discuss relevance to earlier studies.

Reference:

1. S. Zenitani, Phys. Plasmas, 22, 032114 (2015)
2. S. Zenitani and T. Miyoshi, Astrophys. J. Lett., 894, L7 (2020)