Abstract
The formation of positive streamers in a point-to-plane gap filled with atmospheric pressure air and nitrogen under threshold and overvoltage conditions was experimentally investigated using a HSFC PRO 12-bit four-channel ICCD camera. Waveforms of the voltage and current pulses were simultaneously recorded with shooting. Nanosecond voltage pulses with a positive polarity, an amplitude of 8 and 24 kV were applied to the pointed electrode. Under threshold conditions, branching of the streamer in nitrogen was observed. Under the same conditions, a single streamer was formed in air. At a high voltage, only one large streamer was observed in nitrogen and air. The characteristic X-ray radiation produced by runaway electrons likely pre-ionizes the gas ahead of a streamer at a high overvoltage.
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