Streamer mechanism for negative corona current pulses

Current wave forms of initial stages of breakdown and corona formation in a short negative point-to-plane gap have been measured with a nanosecond time resolution in air, O2, and N2 at pressures 13.33–100 kPa, and at various overvoltages. The experiments revealed the existence of a stepped form of negative corona Trichel pulses in O2 at atmospheric pressure. To test existing models for the negative corona pulse formation, effects of changing cathode secondary electron emission were studied using a brass cathode coated by CuI and graphite. It is concluded that a negative corona (Trichel) pulse is associated with the ignition of a cathode-directed streamer in the immediate vicinity of the cathode and the subsequent formation of a glow-discharge-type cathode region at the streamer arrival to the cathode. The implications of these results to negative corona applications are discussed.