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

Abstract

Unraveling the origin of proton beams and ion Bernstein waves is important to understanding kinetic dissipation in the solar wind. Here we focus on their generation mechanisms, rather than their well-studied roles in instabilities and particle heating. We investigate their formation in collisionless plasmas using high-resolution particle-in-cell simulations of compressible turbulence. At magnetohydrodynamic (MHD) scales, compressive fluctuations are damped via transit-time damping (TTD), naturally producing suprathermal electrons and proton beams. At sub-ion scales, quasi-perpendicular fast modes excite multiple branches of ion Bernstein waves, whose properties agree with predictions from the plasma dispersion relation solver. Under solar wind conditions, TTD remains efficient and provides a natural explanation for the super-Alfvénic proton beams measured in situ. Our results demonstrate that compressive fluctuations play a central role in driving cross-scale energy transfer and kinetic dissipation in collisionless plasma turbulence.