Effects of unequal electron–ion temperature on pressure–strain interaction in nearly collisionless turbulent plasmas

A common occurrence in nearly collisionless 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 remains unexplored. We investigate this using five fully kinetic 2.5-dimensional particle-in-cell simulations of undriven decaying turbulence by varying the initial electron-to-ion temperature ratios. By analyzing the species' internal energy density alongside a decomposition of the pressure–strain interaction, 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 average internal energy density for both electrons and ions, where the total deformation channel dominates energy evolution. We discover that 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. By varying the initial temperature ratio, 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 now approximated via only its shear deformation part, and provide a framework for interpreting energy evolution and conversion in turbulent space plasmas where unequal species temperature is the norm.