Fast reconnection in high-Lundquist-number plasmas due to the plasmoid Instability

Thin current sheets in systems of large size that exceed a critical value of Lundquist number are unstable to a super-Alfvenic tearing instability, referred to hereafter as the plasmoid instability. The scaling of the growth rate of the most rapidly growing plasmoid 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 nearly an order of magnitude (for the range of Lundquist numbers considered). This regime of fast reconnection is realizable in a dynamic and highly unstable thin current sheet, without requiring the current sheet to be turbulent. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3264103]