Dynamics of the optical emission from a high-voltage diffuse discharge in a rod-plane electrode system in atmospheric-pressure air

Results are presented from experimental investigations of the dynamics of optical emission from a nanosecond diffuse discharge in a rod-plane electrode system. A study was made of discharges in a 10-cm-long interelectrode gap in atmospheric-pressure air (the cathode being a 1-cm-diameter rod with a bullet-shaped end). The voltage across the discharge gap was 220 kV and the voltage pulse duration was 180 ns, the voltage rise time being 10 ns. In experiments, the discharges were observed to evolve through two stages: the bridging stage and the conduction stage. The bridging stage begins with intense optical emission from the cathode region, the onset of the emission being delayed with respect to the beginning of the voltage pulse. Simultaneously with the onset of optical emission, a displacement current corresponding to the motion of charged particles begins to be generated in the cathode region. The duration of this current corresponds to the time the emission front takes to bridge the gap. As the emission front reaches the anode region, the current increases abruptly, indicating the beginning of the conduction stage. It was found that the time delay of optical emission relative to the beginning of the voltage pulse largely governs the discharge parameters: as the time delay becomes longer, the emission front velocity in the bridging stage increases from 0.6 to 1.5 cm/ns, the probability of realizing a multichannel structure of the discharge becomes higher, and the discharge current and the intensity of X-ray emission from the discharge grow.