Characteristics of negative-polarity DC superimposed nanosecond pulsed discharge and its applications

Non-thermal plasma generated by pulsed discharge is expected to efficiently treat combustion exhaust gases such as nitrogen oxide (NO_x) and sulfur oxide (SOx) due to its high chemical activity. Nanosecond pulsed discharge which has voltage rise time and fall time of 2 ns, pulse width 5 ns and peak value of 60 kV, has been developed by our group. Nanosecond pulsed discharge mainly consists of streamer discharge phase, so that heat loss which caused by glow discharge is less, and plasma impedance is kept almost constant during the streamer discharge phase. Therefore, impedance matching between pulsed power supply and discharge load is possible. Applications on ozone generation and NO treatment using nanosecond pulsed discharge are reported with high energy efficiency compared to other discharge methods. However, the discharge mode transit to arc discharge phase sometimes. Also, for industrial applications, the plasma processing capacity leaves room to improve. It has also been reported that negative polarity nanosecond pulse discharges give better results depending on the plasma processing applications. In this study, negative polarity DC superimposed nanosecond pulsed discharge was suggested in order to improve the better performance of the nanosecond discharge plasma. Results of ozone generation using negative polarity DC superimposed nanosecond pulsed discharge have also been introduced.