Kinetic plasma turbulence during the nonlinear stage of the Kelvin-Helmholtz instability

TL;DR

This study uses kinetic simulations to analyze plasma turbulence at the Earth's magnetosphere interface, revealing spectral cascades, secondary instabilities, and wave phenomena consistent with satellite data.

Contribution

It provides detailed kinetic insights into turbulence mechanisms and spectral behaviors during Kelvin-Helmholtz instability, extending understanding beyond previous models.

Findings

Magnetic energy spectrum matches satellite observations.

Lower hybrid drift instability causes spectral peak beyond electron inertial scale.

Ion-Bernstein waves influence the electric energy spectrum.

Abstract

Using a full kinetic, implicit particle-in-cell code, iPiC3D, we studied the properties of plasma kinetic turbulence, such as would be found at the interface between the solar wind and the Earth magnetosphere at low latitude during northwards periods. In this case, in the presence of a magnetic field B oriented mostly perpendicular to the velocity shear, turbulence is fed by the disruption of a Kelvin-Helmholtz vortex chain via secondary instabilities, vortex pairing and non-linear interactions. We found that the magnetic energy spectral cascade between ion and electron inertial scales, $d_i$ and $d_e$, is in agreement with satellite observations and other previous numerical simulations; however, in our case the spectrum ends with a peak beyond $d_e$ due to the occurrence of the lower hybrid drift instability. The electric energy spectrum is influenced by effects of secondary instabilities: anomalous resistivity, fed by the development of the lower hybrid drift instability, steepens the spectral decay and, depending on the alignment or anti-alignment of B and the shear vorticity, peaks due to ion-Bernstein waves may dominate the spectrum around $d_i$. These waves are generated by counter-streaming flow structures, through flux freezing also responsible for reconnection of the in-plane component of the magnetic field, which then generates electron pressure anisotropy and flattening of the field-aligned component of the electron distribution function.