Diagnostic techniques for atmospheric streamer discharges

Fast electrical and optical diagnostics are required for the analysis of atmospheric streamer discharges. This is illustrated for the case of positive streamer corona produced along wire electrodes by high voltage pulses with rise times of tens of nanoseconds. Electrical measurements with a high time resolution reveal the energy input in two discharge phases (primary and secondary streamer). The discharge structure is visualised using a gated image intensifier. The number of streamers per unit length of anode wire and the streamer diameter are determined. The streamer velocity is measured with a time-of-flight method using two optical fibres. Time-resolved spectroscopic measurements of the intensity ratio of N₂⁺ and N ₂ emission lines reveal that the average electron energy in the primary streamer phase is significantly higher than in the subsequent secondary streamer. The neutral gas temperature in the discharge is determined from the rotational structure of an N₂ emission line and is only slightly above the background gas temperature. Schlieren photographs visualise the heat dissipated in residual streamer channels