Velocity-Space Signatures of Energy Transfer for Ion-Acoustic Instabilities

TL;DR

This paper uses kinetic simulations and the field-particle correlation technique to identify signatures of ion-acoustic instabilities, aiding future detection in solar wind observations despite current sampling limitations.

Contribution

It demonstrates the application of FPC to characterize energy transfer signatures of IIAI in kinetic simulations relevant to the solar wind.

Findings

Identified IIAI signatures in simulations compatible with solar wind conditions.

Proposed diagnostics for recognizing IIAI in spacecraft observations.

Highlighted the challenge of current sampling rates for real-time detection.

Abstract

Context. Observations by Parker Solar Probe (PSP) of electrostatic waves suggest that electrostatic instabilities, including the ion-ion-acoustic instability (IIAI) frequently observed in the inner heliosphere, play an important role in plasma heating and particle acceleration. Aims. Our aim is to explore the application of single spacecraft diagnostics to the IIAI, in anticipation of application to the current missions operating in the inner heliosphere, e.g. PSP and Solar Orbiter. Methods. We apply the field-particle correlation (FPC) technique to fully kinetic simulations of IIAI. We characterize the conversion of energy between the electric field and particle species, allowing the differentiation between oscillatory and secular energy transfer to and from the particles and highlighting the role of resonant energy exchange. We then identify the characteristic IIAI signatures for the proton and electron distributions, and relate them to our previous knowledge of IIAI onset and energy exchange mechanisms. Results. Applying the FPC technique to our simulations run in parameters regime compatible with solar wind conditions, we have identified IIAI signatures that would enable efficient recognition of IIAI in observations. This task is left for future missions, since the time scale over which IIAI signatures develop is too fast for the sampling rates of current missions.