Modelling of transport in non-equilibrium atmospheric plasmas

In traditional low-pressure plasma modelling, the transport of the species of interest is described relative to a stationary and uniform background gas, like helium or argon. The transport flux densities are commonly modelled with a Fick-like diffusion term, augmented with a drift contribution for the charged species. Some modern applications share the non-thermal nature with those discharges, but operate at much higher pressures and are created in flowing compound gases, like air. Examples are the discharges that are presently being considered for biomedical plasma applications. As a result, gas heating can play a role and the concept of a static, abundant background gas may no longer apply. Consequently, existing low-pressure gas discharge models cannot be used unaltered for the simulation of such atmospheric discharges. In this contribution, we will provide an overview of the challenges involved in the successful numerical simulation of such plasmas. The discussion will zoom in on the modelling of the species’ transport fluxes. The conceptual problems of the drift-diffusion model in flowing plasmas will be explained, followed by a presentation of an alternative approach, which is based on the Stefan-Maxwell equations. Special attention will be paid to the numerical aspects of the transport algorithms and the novel discretisation method that we have developed.