Transient Spark Discharges in High-Velocity Airflow

Air-filled, self-breakdown plasma closing switches (PCSs) can operate at high pulse repetition frequency when overstressed with HVdc voltage. However, their recovery characteristics, breakdown voltage, the achievable pulse repetition rate, and variation in this rate are affected by the thermal effects local to the electrodes and by gas by-products generated by spark discharges. As a potential improvement to the performance of PCSs, flowing gas can be forced through the interelectrode gap. In this article, it was shown that purging an interelectrode gap of the plasma closing switch with air is a viable way of controlling the pulse repetition rate and variation of this rate. It was found that the difference between breakdown voltages of the first (single) breakdown events in static air and at 100-m/s airflow was less than 10%. In static air, the breakdown voltage of repetitive breakdown events decreases after the first and reaches its saturation value. It was shown that the introduction of the airflow at 100 m/s leads to recovery of the repetitive breakdown voltage, which could reach its new saturation value, up to 30% higher than the first recorded breakdown voltage. Also, purging of the spark gap with air resulted in decreasing the pulse repetition rate, and however, it leads to higher breakdown voltage, lower variation in pulse repetition rate, and increasing plasma conductivity in the spark channel, thereby increasing the efficiency of the overall high voltage system via reduced switching losses.