Compressible Turbulence as a Source of Particle Beams and Ion Bernstein Waves in Collisionless Plasmas

TL;DR

This paper demonstrates through simulations that compressible turbulence in collisionless plasmas naturally generates particle beams and ion Bernstein waves, explaining observed super-Alfvénic proton beams in the solar wind.

Contribution

It reveals the role of compressible turbulence in producing particle beams and ion Bernstein waves across scales, providing a new understanding of energy transfer in collisionless plasmas.

Findings

Suprathermal electrons and proton beams are generated by transit-time damping.

Ion Bernstein waves are excited at sub-ion scales, forming proton tails.

Processes remain efficient under solar wind conditions.

Abstract

We investigate the source of particle beams and ion Bernstein waves in collisionless plasmas using a high-resolution particle-in-cell simulation of compressible turbulence. At magnetohydrodynamic (MHD) scales, compressible turbulence is damped by transit-time damping, naturally generating suprathermal electrons and proton beams. As the energy cascade reaches sub-ion scales, multiple branches of ion Bernstein waves are excited and contribute to the formation of proton suprathermal tails. Under realistic conditions such as those in the solar wind, these processes remain efficient and provide a natural explanation for the super-Alfv\'enic proton beams observed in situ. We show that compressive fluctuations, though often understudied, are essential for cross-scale energy transfer and dissipation in collisionless plasma turbulence.