Formation and propagation of streamers in ${\mathrm{N}}_2$ and ${\mathrm{N}}_2$-${\mathrm{SF}}_6$ mixtures

In this paper we present results from a self-consistent two-dimensional numerical simulation of the formation and propagation of streamers in nonattaching (${\mathrm{N}}_2$) and attaching (${\mathrm{N}}_2$-${\mathrm{SF}}_6$ mixture) gases using a one-moment fluid model. A numerical technique has been used which allows the solution of the space-charge equations in the presence of large gradients and dynamic range. Photoionization in the gas and photoelectric effect at the cathode have been taken into account. Streamers in the ${\mathrm{N}}_2$-${\mathrm{SF}}_6$ mixture have been found to be considerably different from those in ${\mathrm{N}}_2$. Spatial oscillations in the electron density have been observed for the ${\mathrm{N}}_2$-${\mathrm{SF}}_6$ mixture, which lead to a more complex field distribution and particle-flow dynamics. The results obtained for ${\mathrm{N}}_2$ have been compared to those obtained with use of a kinetic description of the electron dynamics. Comparisons with experimental observations and interpretation of experimental observations have been made for both ${\mathrm{N}}_2$ and ${\mathrm{N}}_2$-${\mathrm{SF}}_6$ mixtures.