High Fidelity Simulations of Non-Equilibrium Plasmas

High energy density (HED) plasmas, especially those which only last for short periods of time, are subject to non-equilibrium phenomena, owing to the inability of individual particles to exchange information between internal energy modes or with other particles. Kinetic simulations, which capture the evolution of individual particles are high-fidelity but have two main limitations: (1) kinetic simulations can be often prohibitively expensive, owing to the wide range of temporal and spatial scales of interest, and (2) HED plasmas often follow a non-ideal equation of state, that is, the internal pressure is not always isotropic and proportional to the energy density. Fluid and hybrid simulations can achieve a computational advantage by considering particles as an ensemble and describing the flow of mass, momentum and energy through the system; however, this typically requires a closure, e.g., an assumption that the plasma is near collisional equilibrium. Recent experiments have observed temperature anisotropies in high-energy laser-induced plasmas, which can affect plasma transport and reaction rates. Conventional fluid models may be limited in capturing these non-equilibrium phenomena. We will present (1) results from 10-moment multi-fluid plasma model that can capture finite non-equilibrium effects through direct modelling of a full anisotropic pressure tensor and (2) results from kinetic simulations that are evolved in tandem with the fluid equations to allow for algorithmic acceleration.