Do chaotic field lines cause fast reconnection in coronal loops?

TL;DR

This study tests Boozer's theory that 3D magnetic field chaos leads to fast reconnection without intense current sheets, using simulations that reveal deviations from the theory's predictions.

Contribution

The paper provides a critical simulation-based evaluation of Boozer's theory, highlighting discrepancies and refining understanding of 3D magnetic reconnection mechanisms.

Findings

Ideal simulations show higher current density than predicted.

Resistive simulations reveal linear scaling of current density with Lundquist number.

Boozer and Elder's model underestimates current intensity due to missing terms.

Abstract

Over the past decade, Boozer has argued that three-dimensional (3D) magnetic reconnection fundamentally differs from two-dimensional (2D) reconnection due to the fact that the separation between any pair of neighboring field lines almost always increases exponentially over distance in a 3D magnetic field. According to Boozer, this feature makes 3D field-line mapping chaotic and exponentially sensitive to small non-ideal effects; consequently, 3D reconnection can occur without intense current sheets. We test Boozer's theory via ideal and resistive reduced magnetohydrodynamic simulations of the Boozer-Elder coronal loop model driven by sub-Alfvenic footpoint motions [A. H. Boozer and T. Elder, Physics of Plasmas 28, 062303 (2021)]. Our simulation results significantly differ from their predictions. The ideal simulation shows that Boozer and Elder under-predict the intensity of current density due to missing terms in their reduced model equations. Furthermore, resistive simulations of varying Lundquist numbers show that the maximal current density scales linearly rather than logarithmically with the Lundquist number.