Viscoresistive plasmoid instability
Abstract
The plasmoid instability in viscoresistive current sheets is analyzed in both the linear and nonlinear regimes. The linear growth rate and the wavenumber are found to scale as S^{1 /4}(1^{+Pm ) 5 /8} and S^{3 /8}(1^{+Pm ) 3 /16} with respect to the Lundquist number S and the magnetic Prandtl number P_{m}. Furthermore, the linear layer width is shown to scale as S^{1 /8}(1^{+Pm ) 1 /16} . The growth of the plasmoids slows down from an exponential growth to an algebraic growth when they enter into the nonlinear regime. In particular, the timescale of the nonlinear growth of the plasmoids is found to be τN_{L}∼S^{3 /16}(1^{+Pm) 19 /32}τA_{,L} . The nonlinear growth of the plasmoids is radically different from the linear one, and it is shown to be essential to understand the global current sheet disruption. It is also discussed how the plasmoid instability enables fast magnetic reconnection in viscoresistive plasmas. In particular, it is shown that the recursive plasmoid formation can trigger a collisionless reconnection regime if S ≳L_{c s}(ɛ^{clk) 1}(1^{+Pm) 1 /2} , where L_{cs} is the halflength of the global current sheet and l_{k} is the relevant kinetic length scale. On the other hand, if the current sheet remains in the collisional regime, the global (timeaveraged) reconnection rate is shown to be <d_{ψ/d t  X} > ≈ɛ_{c}v_{A ,u}B_{u}(1^{+Pm) 1 /2} , where ɛ_{c} is the critical inverse aspect ratio of the current sheet, while v_{A,u} and B_{u} are the Alfvén speed and the magnetic field upstream of the global reconnection layer.
 Publication:

Physics of Plasmas
 Pub Date:
 March 2016
 DOI:
 10.1063/1.4942940
 arXiv:
 arXiv:1603.00090
 Bibcode:
 2016PhPl...23c2111C
 Keywords:

 Physics  Plasma Physics;
 Astrophysics  High Energy Astrophysical Phenomena;
 Astrophysics  Solar and Stellar Astrophysics;
 Physics  Space Physics
 EPrint:
 Published in Physics of Plasmas