Fast Reconnection in High-Lundquist-Number Plasmas Due to Secondary Tearing Instabilities

TL;DR

This paper demonstrates that secondary tearing instabilities in large, thin current sheets lead to fast magnetic reconnection rates that are weakly dependent on the Lundquist number, surpassing classical models without turbulence.

Contribution

It shows that secondary tearing instabilities cause fast reconnection in high-Lundquist-number plasmas, challenging traditional slow reconnection models like Sweet-Parker.

Findings

Reconnection rate exceeds Sweet-Parker by an order of magnitude.

Growth rate scales with Lundquist number following classical tearing mode dispersion.

Fast reconnection occurs without turbulence in thin current sheets.

Abstract

Thin current sheets in systems of large size that exceed a critical value of the Lundquist number are unstable to a super-Alfvenic tearing instability. The scaling of the growth rate of the fastest growing instability with respect to the Lundquist number is shown to follow from the classical dispersion relation for tearing modes. As a result of this instability, the system realizes a nonlinear reconnection rate that appears to be weakly dependent on the Lundquist number, and larger than the Sweet-Parker rate by an order of magnitude (for the range of Lundquist numbers considered). This regime of fast reconnection appears to be realizable in a dynamic and highly unstable thin current sheet, without requiring the current sheet to be turbulent.