Driving frequency effects on the atmospheric pressure corona jet discharge

Abstract

The atmospheric pressure corona plasma has been widely applied to various fields over the last century, and it is probably one of the most important discharge types in the industry. Yet, its physical and chemical properties have not been fully understood. Especially, the driving frequency effects on the corona discharge characteristics have seldom been investigated despite the fact that the driving frequency is one of the key parameters governing the plasma characteristics. Hence, in this thesis, dependence of the plasma characteristics on the driving frequency was explored from low frequency (LF: several tens of kHz) to radio frequency (RF: MHz) in a simple corona system of single pin electrode structure. LF (5 - 75 kHz) corona jet plasmas were cylindrical shape of several tens of mm`s long when observed with naked eyes, but when viewed through time-resolved images, they exhibited positive streamer and negative glow for each half period. Interestingly, multi-streamers consisting of two streamer heads were observed unlike the previous reports. The initial streamer appeared when the input voltage was as low as 0 V, and we suggest that the space charge accumulated during the discharge of the previous period results in the appearance of the initial streamer in the next period based on various experimental measurements. The atmospheric pressure corona jet plasmas were also generated by RF (2 - 13.56 MHz). They showed several distinctive discharge characteristics compared to LF; first, the plasma length became shortened as the driving frequency was increased. Second, while the plasmas generated by the frequency under 2 MHz have different discharge modes for each half period, the negative glow and the positive streamer, the discharge was more continuous in time for the 13.56 MHz plasma. Third, it was inferred from the measured I-V curves that the higher driving frequency induced the higher discharge current. Finally, the gas temperature was increased as the driving...