Bi-Directional Energy Cascades and the Origin of Kinetic Alfv\'enic and Whistler Turbulence in the Solar Wind

TL;DR

This paper investigates how energetic electrons in the solar wind generate kinetic Alfvénic and whistler turbulence through plasma instabilities and energy cascades, using particle-in-cell simulations.

Contribution

It demonstrates that free energy from energetic electrons can drive electromagnetic waves leading to turbulence via wave interactions and cascades, a novel insight into solar wind turbulence origins.

Findings

Energetic electrons induce electromagnetic waves via two-stream instability.

Wave-wave interactions lead to kinetic Alfvénic and whistler turbulence.

Energy cascades transfer magnetic energy across scales.

Abstract

The observed sub-proton scale turbulence spectrum in the solar wind raises the question of how that turbulence originates. Observations of keV energetic electrons during solar quite-time suggest them as possible source of free energy to drive the turbulence. Using particle-in-cell simulations, we explore how free energy in energetic electrons, released by an electron two-stream instability drives Weibel-like electromagnetic waves that excite wave-wave interactions. Consequently, both kinetic Alfv\'enic and whistler waves are excited that evolve through inverse and forward magnetic energy cascades.