Fully Kinetic Simulations of Proton-Beam-Driven Instabilities from Parker Solar Probe Observations

TL;DR

This study uses fully kinetic simulations to analyze proton velocity distribution functions observed by Parker Solar Probe, revealing how proton-beam instabilities lead to wave interactions and perpendicular heating in the solar wind.

Contribution

It introduces a 2.5D kinetic simulation approach to investigate proton-beam instabilities driven by PSP observations, highlighting the wave-particle interactions and heating mechanisms.

Findings

Proton-beam instability triggers nearly parallel fast magnetosonic modes.

Resonant wave interactions cause perpendicular heating of protons.

Instability development leads to wave-particle energy exchange before saturation.

Abstract

The expanding solar wind plasma ubiquitously exhibits anisotropic non-thermal particle velocity distributions. Typically, proton Velocity Distribution Functions (VDFs) show the presence of a core and a field-aligned beam. Novel observations made by Parker Solar Probe (PSP) in the innermost heliosphere have revealed new complex features in the proton VDFs, namely anisotropic beams that sometimes experience perpendicular diffusion. In this study, we use a 2.5D fully kinetic simulation to investigate the stability of proton VDFs with anisotropic beams observed by PSP. Our setup consists of a core and an anisotropic beam populations that drift with respect to each other. This configuration triggers a proton-beam instability from which nearly parallel fast magnetosonic modes develop. Our results demonstrate that before this instability reaches saturation, the waves resonantly interact with the beam protons, causing perpendicular heating at the expense of the parallel temperature.