Kinetic plasma turbulence: recent insights and open questions from 3D3V simulations

TL;DR

This paper reviews recent advances in 3D3V kinetic plasma turbulence simulations, comparing freely decaying and driven fluctuations, and discusses open questions and future directions in understanding space plasma turbulence at kinetic scales.

Contribution

It provides a comprehensive analysis of recent 3D3V kinetic simulations of plasma turbulence, highlighting similarities and differences in sub-ion range properties and identifying open research questions.

Findings

Simulations reveal differences between freely decaying and driven turbulence.

Kinetic simulations help interpret spacecraft measurements at plasma scales.

Open questions remain about dissipation mechanisms in collisionless plasmas.

Abstract

Turbulence and kinetic processes in magnetized space plasmas have been extensively investigated over the past decades via \emph{in-situ} spacecraft measurements, theoretical models and numerical simulations. In particular, multi-point high-resolution measurements from the \emph{Cluster} and \emph{MMS} space missions brought to light an entire new world of processes, taking place at the plasma kinetic scales, and exposed new challenges for their theoretical interpretation. A long-lasting debate concerns the nature of ion and electron scale fluctuations in solar-wind turbulence and their dissipation via collisionless plasma mechanisms. Alongside observations, numerical simulations have always played a central role in providing a test ground for existing theories and models. In this Perspective, we discuss the advances achieved with our 3D3V (reduced and fully) kinetic simulations, as well as the main questions left open (or raised) by these studies. To this end, we combine data from our recent kinetic simulations of both freely decaying and continuously driven fluctuations to assess the similarities and/or differences in the properties of plasma turbulence in the sub-ion range. Finally, we discuss possible future directions in the field and highlight the need to combine different types of numerical and observational approaches to improve the understanding of turbulent space plasmas.