Two-dimensional nonequilibrium fluid models for streamers

The self-consistent, two-dimensional fluid simulation for describing nitrogen gap pre-breakdown phenomena under atmospheric pressure has been presented in cylindrically symmetric geometry. The models of the electron dynamics are characterized either by an equilibrium single-moment equation or by a nonequilibrium three-moment equation. A more accurate flux-corrected transport (MAFCT) technique, which provides the solution with steep and varying gradients in large dynamic ranges, is used to solve the electron fluid equations. This is the first time that the spatial-temporal two dimensional (r,z) simulation results of the development and propagation of streamers are presented based on a nonequilibrium multidimensional fluid model. Included in the step-by-step presentation are the electron density, the space-charge electric field, the electron average velocity, the electron mean energy, and the electron power deposition form the initial stage to the later stage when the ionizing channel bridges the gap. The differences between equilibrium and nonequilibrium fluid models are discussed in terms of the formation of ionizing channels and the propagation of streamers. Moreover, the validity of fluid models is assessed by a Monte Carlo simulation result (a kinetic model); the comparison results agree with the analysis that the non-equilibrium fluid model is a more accurate description for streamers than the equilibrium fluid model