Propagation of a positive streamer discharge along a dielectric rod*

We simulate positive streamer discharges developing in artificial air near dielectric and conductive materials. This research is important, for example, in the high voltage technology where surface flashovers are to beavoided. We designed an axially symmetric model in which a positive streamer develops at the tip of the needle electrode (parameterized as a spheroid) and propagates towards and then along a dielectric rod (a cylinder). Our model includes field modification due to the polarization effect, photoionization, charge accumulation on the dielectric surface and photoelectron emission. We describe a numerical method (a generalized Ghost Fluid Method) which allowed us to include dielectric interfaces into our streamer model, in an accurate and fast manner. Finally, we measure the velocity of a positive streamer propagating along the dielectric rod and compare it with experiments. We discuss the importance of the surface photoelectron emission as an intrinsically non-local source of free electrons for streamer propagation.