Modeling interface dynamics in kinetic plasmas with the Ellipsoidal BGK model

The multispecies Bhatnagar-Gross-Krook (BGK) collisional model is suited to modeling kinetic effects in warm dense matter, where the weak coupling assumptions underpinning traditional kinetic plasma models break down. One significant drawback of the standard BGK approximation is that thermalization due to collisions is applied isotropically, which poorly models situations where one expects a more anisotropic distribution, such as particle beams or diffusion generated by an electric field at an interface. In this talk, I will explore the extension of the Ellipsoidal BGK model (commonly appreviated as ES-BGK), which uses the pressure tensor of the distribution function to allow for local relaxaiton to an Ellipsoidal gaussian. I will compare to the standard BGK model in interfaces in ICF-like regimes as well as phase space data from moderately coupled ultracold neutal plasma experiments. (LA-UR-25-28188)