Transition from primary streamer to arc in negative point-to-plane corona

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Abstract
This paper reports on measurements with multiple techniques delineating the complete sequence of events from the primary streamer to the arc phase in the common spark transition for relatively small negative point‐to‐plane gaps applied by pulsed potential. The observations cover a range of gaps, in room air, from 3 to 7 cm long, covering the whole range of potentials from streamer onset to in excess of 30% above the standard sparking threshold. It is shown that starting with the primary streamer, which usually fades in midgap and occasionally crosses the gap, the secondary and tertiary streamers are produced by a succession of ionizing waves of potential and due to an increase of the potential applied across the gap. If overvoltage exceeds 30%, the tertiary streamer comes close to the anode and induces return ionizing waves, which lead to the thermalization of the arc. At lower overvoltages there is a dark phase lasting for about 10 μsec. During the dark period, the resultant positive ions and electrons move separately to the cathode and to the anode. The arrival of these new electrons at the plane causes very fast luminous ionizing waves which lead to the thermalization of the arc. After the last pulse, the thermalization follows through gas heating for a time from 100 to 150 nsec.

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