Electrostatic Bursts Generated by the Ion-Ion Acoustic Instability with Solar Wind Plasma Parameters

TL;DR

This paper investigates the ion-ion acoustic instability's role in generating electrostatic bursts in solar wind plasma, using linear theory and kinetic simulations to match recent Parker Solar Probe observations.

Contribution

It demonstrates that ion-ion acoustic instability can produce observed electrostatic bursts in solar wind conditions, supported by theoretical analysis and kinetic simulations.

Findings

IAI can occur in PSP-relevant plasma regimes

Simulations confirm predicted growth rates and saturation behaviors

Nonlinear structures resemble observed electrostatic bursts

Abstract

This study is motivated by recent observations from the Parker Solar Probe (PSP) mission, which have been identified as the ion-acoustic waves from 15 to 25 solar radii. These observations reveal characteristic sequences of narrow-band, high-frequency bursts exceeding 100 Hz embedded into a slower evolution around 1 Hz, persisting for several hours. To explore the potential role of the ion-acoustic instability (IAI) in these phenomena, we begin by reviewing classical findings on the IAI within the framework of linear kinetic theory. Focusing on proton distributions comprising both a core and a beam component, we analyze the IAI instability range and growth rates within the parameter regime relevant to PSP observations. Our findings indicate that the IAI can indeed occur in this regime, albeit requiring electron-to-core and beam-to-core temperature ratios slightly different from reported values during electrostatic burst detection. Furthermore, employing 1D kinetic plasma simulations, we validate the growth rates predicted by linear theory and observe the saturation behavior of the instability. The resultant nonlinear structures exhibit trapped proton beam populations and oscillatory signatures comparable to those observed, both in terms of time scales and amplitude.