Magnetic reconnection as a driver for a sub-ion scale cascade in plasma turbulence

TL;DR

This study reveals that magnetic reconnection triggers a sub-ion scale cascade in collisionless plasma turbulence, producing a stable power-law spectrum independent of large-scale turbulence development.

Contribution

It uncovers a new mechanism where magnetic reconnection initiates sub-ion scale cascades, supported by high-resolution hybrid-kinetic simulations with different approaches.

Findings

Reconnection events trigger sub-ion scale power-law spectra.

The small-scale spectrum has a stable slope of ~-2.8 during reconnection.

Total magnetic fluctuations follow a -5/3 spectrum at MHD scales and ~-3 at sub-ion scales.

Abstract

A new path for the generation of a sub-ion scale cascade in collisionless plasma turbulence, triggered by magnetic reconnection, is uncovered by means of high-resolution two-dimensional hybrid-kinetic simulations employing two complementary approaches, Lagrangian and Eulerian, and different driving mechanisms. The simulation results provide clear numerical evidences that the development of power-law energy spectra below the so-called ion break occurs as soon as the first magnetic reconnection events take place, regardless of the actual state of the turbulent cascade at MHD scales. In both simulations, the reconnection-mediated small-scale energy spectrum of parallel magnetic fluctuations exhibits a very stable spectral slope of ~-2.8, whether or not a large-scale turbulent cascade has already fully developed. Once a quasi-stationary turbulent state is achieved, the spectrum of the total magnetic fluctuations settles towards a spectral index of -5/3 in the MHD range and of ~-3 at sub-ion scales.