The breakdown of a positive point to plane gap in air near atmospheric pressure begins with the formation of a low-conductivity filament by the space-charge-controlled streamer process. Within the filament, the rate of electron attachment exceeds that of ionization, and the external current decreases. However, a sudden rise of current leading to spark breakdown can be observed. The following explanation is proposed. Owing to the current flow the temperature increases within the discharge. A radial flow of neutral species will thus appear, which decreases the neutral density near the discharge axis. In turn E/N increases until the ionization rate becomes greater than that of attachment, leading to the final current growth. Journal of Applied Physics is copyrighted by The American Institute of Physics.

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