Grid-based Vlasov simulation of collisionless plasma expansion

Abstract

Grid-based Vlasov simulations are carried out to re-evaluate the one-dimensional collisionless plasma expansion into vacuum. The grid-based method eliminates the inherent statistical noise in particle-based methods and allows us to extend the solution beyond the self-similar expansion region and resolve small electron timescale wave perturbations. It is shown that the expansion generates both an ion-acoustic rarefaction wave mode and an electron Langmuir wave mode that propagate into the unperturbed plasma upstream. The assumption used in the classical expansion solution that the electrons are an isothermal fluid is accurate within a quasi-neutral, self-similar expansion region but fails in both the upstream and downstream of that region due to electron timescale perturbations.