Evidence for Electron Landau Damping in Space Plasma Turbulence

TL;DR

This paper demonstrates the use of a field-particle correlation technique to directly observe electron Landau damping in Earth's magnetosheath, providing evidence for a key plasma heating process in space turbulence.

Contribution

It introduces and applies a novel measurement technique to detect electron Landau damping directly in space plasma turbulence.

Findings

Signature of Landau damping observed near resonant velocity

Energy transfer is coherent over time and disappears with phase randomisation

Electron Landau damping likely contributes significantly to plasma heating

Abstract

How turbulent energy is dissipated in weakly collisional space and astrophysical plasmas is a major open question. Here, we present the application of a field-particle correlation technique to directly measure the transfer of energy between the turbulent electromagnetic field and electrons in the Earth's magnetosheath, the region of solar wind downstream of the Earth's bow shock. The measurement of the secular energy transfer from the parallel electric field as a function of electron velocity shows a signature consistent with Landau damping. This signature is coherent over time, close to the predicted resonant velocity, similar to that seen in kinetic Alfv\'en turbulence simulations, and disappears under phase randomisation. This suggests that electron Landau damping could play a significant role in turbulent plasma heating, and that the technique is a valuable tool for determining the particle energisation processes operating in space and astrophysical plasmas.