Effect of CO2 concentration on discharge characteristics under non-uniform DC field in atmospheric air

The effect of CO₂ concentration on discharge characteristics in atmospheric air was investigated under nonuniform DC field gap. In the experiment, positive DC voltage was applied to 2.0 cm of needle-plane gap in air with CO₂ at atmospheric pressure. As a result, a drastic decrease of the withstand voltage of air caused by a dilute increase of CO2 concentration was confirmed. In addition, it was observed that the dilute CO2 mixing in air made streamer corona likely to occur as substitute for occurrence of steady-glow corona. Furthermore, the occurrence frequency of the streamer corona increased with increasing the applied voltage, and the branches of the streamer corona decreased with increasing the frequency of the streamer corona. Eventually, just below sparkover voltage, the branched streamer corona changed to a single liner discharge channel (SLDC). By gas temperature measurement with a spectroscopic measurement system, it was revealed that the transition to SLDC was progressed with increasing background gas heating due to the high frequency branched streamer corona. In consequence, it can be considered that an increase of reduced electric field (E/N) between gap due to the background gas heating caused by the repetitive streamer conduces the decrease in withstand voltage of air.