Influence of ion-to-electron temperature ratio on tearing instability and resulting subion-scale turbulence in a low-βe\beta_e collisionless plasma

Abstract

A two-field gyrofluid model including ion finite Larmor radius (FLR) corrections, magnetic fluctuations along the ambient field and electron inertia is used to study two-dimensional reconnection in a low βe\beta_e collisionless plasma, in a plane perpendicular to the ambient field. Both moderate and large values of the ion-to-electron temperature ratio τ\tau are considered. The linear growth rate of the tearing instability is computed for various values of τ\tau, confirming the convergence to reduced electron magnetodynamics (REMHD) predictions in the large τ\tau limit. Comparisons with analytical estimates in several limit cases are also presented. The nonlinear dynamics leads to a fully-developed turbulent regime that appears to be sensitive to the value of the parameter τ\tau. For τ=100\tau = 100, strong large-scale velocity shears trigger Kelvin-Helmholtz instability, leading to the propagation of the turbulence through the separatrices, together with the formation of eddies of size of the order of the electron skin depth. In the τ=1\tau = 1 regime, the vortices are significantly smaller and their accurate description requires that electron FLR effects be taken into account

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