Energy transfer in positive streamers

Abstract

A Schlieren optical system has been used to measure changes in neutral density in a point-plane gap, during and following positive streamers in air. The results show that energy is transferred to the air molecules by two processes. Electron-neutral elastic collisions during the streamer generate a shock-front which moves radially outwards at around 350 m s-1. Following the streamer current pulse,which lasts for around 0.1 mu s, positive ions drifting towards the negative plane transfer their energy to the neutrals over a period of tens of mu s. This positive ion transfer generates the corona wind and the schlieren technique allows the wind speed to be measured close to the point. Corona wind speeds were found to be in the range 8 to 12 m s-1.