The effects of air flow on the nanosecond pulsed pin-to-pin discharge dynamics in atmosphere-pressure air

Physics of Plasmas, Volume 28, Issue 5, May 2021. Investigation of the breakdown phase of a nanosecond pulsed pin-to-pin discharge in air at atmosphere pressure with different gas flow rates is carried out. The experimental results show that the air flow leads to increase in the breakdown delay time. The effect of air flow rate on the current growth rates and streamer channel appearance at the beginning of breakdown is observed, which indicates that the redistribution and decrease in the densities of reactive species produced by previous discharges are playing the main role in the discharge delay time. When 15 standard liters per minute (slm) air flow is used and pulse frequency is 1 kHz, the discharge current reaches a peak of about 0.5 A, then it decreases to 0.4 A and lasts for about 70 ns, and then the discharge current starts to increase rapidly at a rate of >0.1 A/ns. For pulse frequency of 8 kHz or nitrogen as working gas, the discharge current increases monotonically. Besides, the difference of the gas temperature for the cases of 0 and 15 slm is measured, and the result indicates that the difference of the gas temperature should not be the main contributor to the difference of the breakdown delay time. Detailed analysis shows that the appearance of the first current peak is due to the fast detachment of O2−. Finally, simulation results show that the ionization rate for the case of 15 slm is also more significantly delayed than the case of 0 slm, which is consistent with the measured discharge current waveform.