Imaging and simulations of positive surface and airborne streamers adjacent to dielectric material

[Display omitted] •Intriguing observation of positive airborne streamers originating in a distance from HV electrode is shown.•The experiments were based on optical imaging and electrical discharge recording.•The surface and airborne streamers were propagating along the dielectric surface.•Surface charge accumulation is expected to be origin of airborne streamers.•2D simulations were supporting the hypothesis about origin of the airborne streamers. This paper presents the imaging and simulations of positive airborne and surface streamers in the air that is adjacent to a dielectric material. The goal of this paper is to investigate the intriguing observation of the occurrence of airborne streamers that originate at a dielectric surface at a distance from the tip of a high-voltage electrode. This effect may be attributed to the accumulation of charges at a spot on the dielectric material during subsequent streamers. Such a positively charged spot causes airborne streamer inception after reaching the critical value of the charge density. This effect is observed in a side-view configuration by high-speed imaging in a time-accumulated and spatially resolved mode. The hypothesis of the occurrence of airborne streamers in certain sequences was complemented by 2D simulations. The surface charge densities were quantitatively evaluated by the simulations. Two types of streamers were simulated: first – without an accumulated surface charge; and second – with a spot of a defined charge density (which triggers the airborne streamer). After reaching the critical value of the charge density, such spots that are charged during subsequent cathode-directed streamer events may trigger a discharge towards the air side. The length of the surface streamer along the dielectric surface is voltage-dependent. The experimental and simulation results extend the insight to streamer mechanism in configurations with charges accumulated on the dielectric surface – including the inception of an airborne streamer.