Effects of Unequal Electron-Ion Plasma Beta on Pressure-Strain Interaction in Turbulent Plasmas

TL;DR

This study uses kinetic simulations to explore how unequal electron-ion temperatures influence pressure-strain interactions and energy transfer in turbulent space plasmas, revealing species-specific deformation mechanisms.

Contribution

It provides the first detailed analysis of pressure-strain behavior under thermal disequilibrium in turbulent plasmas, highlighting the dominant role of shear deformation in electron heating.

Findings

Shear deformation primarily governs electron internal energy changes.

Ion deformation contributions largely cancel out, resulting in smaller net effects.

Local deformation characteristics are altered but retain qualitative trends.

Abstract

A common occurrence in weakly collisional space plasmas is the unequal electron-ion temperatures. The pressure-strain interaction provides a mechanism-agnostic pathway for increasing plasma internal energy through spatiotemporally local isotropic compression and volume preserving deformation, yet its behavior under thermal disequilibrium is largely unexplored. We investigate this using five fully kinetic two-dimensional particle-in-cell simulations of undriven decaying turbulence by varying the initial electron-to-ion temperature ratio. By analyzing the species' internal energy density alongside a decomposition of the pressure-strain term, with a focus on the volume-preserving deformation that contains normal and shear contributions, we quantify how the initial temperature imbalance modifies the channels through which turbulence increases each species' internal energy density. The cumulative pressure-strain interaction tracks the change in internal energy for both electrons and ions, with the total deformation channel of energy conversion dominating. We discover that local changes to electron internal energy density are governed primarily by the shear deformation power density, concentrated in electron-scale current sheets, while the ion shear and normal deformation components cancel, yielding a much smaller net deformation power density that peaks around, rather than within, those electron-scale current structures. We find that the amplitudes and localization of deformation change, but preserve these qualitative trends. Together, these results show how thermal disequilibrium could shape species-dependent turbulent "heating rate", measured via pressure-strain interaction and approximated via only its shear deformation part, and provide a framework for interpreting energy evolution and conversion in space plasmas where unequal species temperature is the norm.