On the Anomalous Contribution to the Electric Field in Turbulent Collisionless Plasmas

In plasma physics, one of the main obstacles to unravelling the mechanisms responsible for energy transfer between electromagnetic fields and plasma particles is the multiscale nature of plasma phenomena. In this context, plasma turbulence plays a fundamental role because it transports energy across spatial scales from the energy injection scales (large-scales) down to small-scales at which energy is dissipated. One of the key open challenges in plasma turbulence research is understanding how the small-scale turbulent dynamics couple into and influences the large-scale behaviour of the system and how that influences the energy budget and energy transport at system scales. One approach to address this challenge is to employ so-called Large Eddy Simulations, where the large scales of the system are directly simulated, and the small-scale anomalous dynamics are parameterized using Sub-Grid-Scale (SGS) models for the anomalous contributions. However, the appropriate SGS models for describing collisionless plasma systems with large scale separations remain poorly constrained.

In this work, we employ a series of Vlasov-Hybrid simulations modelling conditions similar to turbulence in Earth’s magnetosheath to characterize the anomalous contributions to the total electric field from each term in the generalized Ohm’s law for different plasma conditions. We discuss the role of anomalous (turbulent) resistivity and anomalous viscosity on the total electric field, and we show that the most relevant anomalous contribution comes from the Hall term for plasmas with low plasma beta. We provide insight on how to model SGS terms in collisionless plasmas at scales within the kinetic range where terms associated with sub-ion physics are not necessarily negligible. To do this we establish the dependence of the anomalous terms on resolved quantities such as the magnetic field, electric current density and plasma vorticity and we evaluate their contribution to the magnetic field generation. Since electric fields strongly contribute to plasma particle energization, our results are relevant for better understanding the cross-scale energy transfer and the anomalous contribution to the energy budget.