Detecting the Fine Structure of Ionization Waves of Positive Streamers

New data on the fine structure of the ionization wave was obtained under conditions of free and surface streamer discharges in air at moderate pressures (30–150 Torr). Using high-speed photography, it was shown that the streamer head consists of a bright main ionization wave and a less bright glow of the main wave precursor, the distance between which depends on the streamer propagation conditions, and that the shape of the wave precursor is close to the shape of the main wave. Differences in the spectral composition of the main ionization wave and its precursor are determined. The facts found should be used to make additions to the model of the cathode-directed streamer.