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

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 E~eff~0.02 independently of S for S>>10⁴. The plasmoid flux (Ψ) and half-width (w_x) distribution functions scale as f(Ψ)~Ψ^-2 and f(w_x)~w_x^-2. The joint distribution of Ψ and w_x shows that plasmoids populate a triangular region w_x>~Ψ/B₀, where B₀ is the reconnecting field. It is argued that this feature is due to plasmoid coalescence. Macroscopic ``monster'' plasmoids with w_x~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.