The scaling of collisionless magnetic reconnection in an electron–positron plasma with non-scalar pressure

Abstract

Collisionless magnetic reconnection via tearing instability in non-relativistic electron-positron (pair) plasma with an anisotropic pressure is investigated. The equilibrium magnetic field is considered to be sheared force-free, and a set of linearized collisionless Magnetohydrodynamics equations describes the evolution of reconnection dynamics. A linear analytical analysis, based on scaling, demonstrates that in such a pair plasma, breaking the frozen in flow constraint for field lines can be mainly provided by the non-gyrotropic pressure of electrons and positrons (rather than the particle bulk inertia) when the current sheet width is smaller than the particle Larmor radius (Δx < r L ). This condition is satisfied when β > d 2 (d = c/ω p is the particle skin-depth with the electron/positron frequency ω p and β = 8πP (0) /B 2 0 Ӷ 1). Meanwhile, on top of the Lorentz force and in the absence of the reconnection facilitating mechanism of the Hall effect, non-scalar pressure force can accelerate bulk plasma into the diffusion region at the scale lengths of the order of d. Therefore, the respective regime of tearing instability proceeds much faster compared with the case of an isotropic pressure with a new dimensionless growth rate of (γτ A ) ∼ d.

The scaling of reconnection rate in the two-fluid model of a collisionless forced magnetic reconnection

“…Magnetic reconnection can proceed either via the tearing instability (spontaneous reconnection) (Furth et al 1963;Terasawa 1983;Shukla et al 1996Shukla et al , 1999Fitzpatrick and Porcelli 2004;Hosseinpour et al 2009Hosseinpour et al , 2013 or by the influence of an externally driven perturbation in MHD stable configuration (forced reconnection) (Hahm and Kulsrud 1985;Wang and Bhattacharjee 1992;Avinash, et al 1998;Birn, et al 2005;Vekstein and Bian 2006). Usually the forced reconnection is analyzed under the so-called Taylor model: A tearing stable slab of plasma is subjected to a small external boundary deformation that triggers magnetic reconnection at the neutral magnetic surface within the plasma volume.…”