Magnetic reconnection and stochastic plasmoid chains in high-Lundquist-number plasmas

Abstract

A numerical study of magnetic reconnection in the large-Lundquist-number (S), plasmoid-dominated regime is carried out for S up to 107. The theoretical model of Uzdensky et al. [Phys. Rev. Lett. 105, 235002 (2010)] is confirmed and partially amended. The normalized reconnection rate is Ẽeff∼0.02 independently of S for S≫104. The plasmoid flux (Ψ) and half-width (wx) distribution functions scale as f(Ψ)∼Ψ-2 and f(wx)∼wx-2. The joint distribution of Ψ and wx shows that plasmoids populate a triangular region wx≳Ψ/B0, where B0 is the reconnecting field. It is argued that this feature is due to plasmoid coalescence. Macroscopic “monster” plasmoids with wx∼10% of the system size are shown to emerge in just a few Alfvén times, independently of S, suggesting that large disruptive events are an inevitable feature of large-S reconnection.