Magnetic reconnection: Self-similar current sheet collapse triggered by "ideal" tearing

Abstract

We study, by means of MHD simulations, the onset and evolution of fast reconnection via the "ideal" tearing mode within a collapsing current sheet at high Lundquist numbers ($S\gg 10^4$). We first confirm that as the collapse proceeds, fast reconnection is triggered well before a Sweet-Parker type configuration can form: during the linear stage plasmoids rapidly grow in a few Alfvén times when the predicted "ideal" tearing threshold $S^{-1/3}$ is approached from above; after the linear phase of the initial instability, X-points collapse and reform nonlinearly. We show that these give rise to a hierarchy of tearing events repeating faster and faster on current sheets at ever smaller scales, corresponding to the triggering of "ideal" tearing at the renormalized Lundquist number. In resistive MHD this process should end with the formation of sub-critical ($S\le 10^4$) Sweet Parker sheets at microscopic scales. We present a simple model describing the nonlinear recursive evolution which explains the timescale of the disruption of the initial sheet.

Accepted for publication to the ApJL

References in corpus (4)

• Instability of current sheets and formation of plasmoid chains
• Self-Feeding Turbulent Magnetic Reconnection on Macroscopic Scales
• A catastrophe model for fast magnetic reconnection onset
• The tearing mode instability of thin current sheets: the transition to fast reconnection in the presence of viscosity

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