Role of reconnection in inertial kinetic-Alfvén turbulence

Abstract

In a weakly collisional, low-electron-beta plasma, large-scale Alfvén turbulence transforms into inertial kinetic-Alfvén turbulence at scales smaller than the ion microscale (gyroscale or inertial scale). We propose that at such kinetic scales, the nonlinear dynamics tends to organize turbulent eddies into thin current sheets, consistent with the existence of two conserved integrals of the ideal equations, energy and helicity. The formation of strongly anisotropic structures is arrested by the tearing instability that sets a critical aspect ratio of the eddies at each scale a in the plane perpendicular to the guide field. This aspect ratio is defined by the balance of the eddy turnover rate and the tearing rate, and varies from (de/a)1/2 to de/a depending on the assumed profile of the current sheets. The energy spectrum of the resulting turbulence varies from k-8/3 to k-3, and the corresponding spectral anisotropy with respect to the strong background magnetic field from kzk2/3 to kzk.