Modeling ion beams, kinetic instabilities, and waves observed by the Parker Solar Probe near perihelia

TL;DR

This paper combines observations from the Parker Solar Probe with hybrid-PIC simulations to study ion beams, kinetic instabilities, and wave activity near perihelia, shedding light on solar wind heating mechanisms.

Contribution

It presents the first detailed modeling of ion velocity distribution functions and kinetic instabilities driven by ion beams in the inner heliosphere near perihelia.

Findings

Ion beams drive kinetic instabilities in the solar wind.

Energy partitioning between particles and magnetic fields is characterized.

Ion beam-driven instabilities contribute significantly to solar wind plasma heating.

Abstract

Recent in-situ observations from the Parker Solar Probe (PSP) mission in the inner heliosphere near perihelia show evidence of ion beams, temperature anisotropies, and kinetic wave activity, which are likely associated with kinetic heating and acceleration processes of the solar wind. In particular, the proton beams were detected by PSP/SPAN-I and related magnetic fluctuation spectra associated with ion-scale waves were observed by the FIELDS instrument. We present the ion velocity distribution functions (VDFs) from SPAN-I and the results of 2.5D and 3D hybrid-particle-in-cell (hybrid-PIC) models of proton and alpha particle super-Alfvenic beams that drive ion kinetic instabilities and waves in the inner-heliospheric solar wind. We model the evolution of the ion VDFs with beams, ion relative drifts speeds, and ion temperature anisotropies for solar wind conditions near PSP perihelia. We calculate the partition of energies between the particles (ions) along and perpendicular to the magnetic field, as well as the evolution of magnetic energy and compare to observationally deduced values. We conclude that the ion beam driven kinetic instabilities in the solar wind plasma near perihelia are important components in the cascade of energy from fluid to kinetic scale, an important component in the solar wind plasma heating process.