Study of cathode-directed positive streamers in air by streamer current and luminosity measurements

An experimental set-up with a quasi-uniform DC electric field distribution between two plane parallel electrodes has been constructed to investigate the cathode-directed positive streamers in air. Measurements of the streamer currents on both sides of the electrode gap have been performed and analysed. The propagation characteristics of a streamer initiated from a point on the anode and reaching the cathode have been obtained. The average streamer velocity is determined from the streamer current diagrams and the luminosity oscillograms using fiber optical measurements. The streamer velocity has been found to be linearly dependent on the DC electric field of the gap. The ratio of the amplitudes of the streamer currents on both sides of the electrode gap is also dependent on the average DC electric field of the gap. The magnitude of the DC electric field sustaining a streamer keeping the same current amplitude while propagating in the gap is found to be 430 kV/m. Comparison is made with previously published works.