The driving frequency effects on the atmospheric pressure corona jet plasmas from low frequency to radio frequency

Lately, the atmospheric pressure jet type corona plasma, which has been typically driven by dc to low frequency (LF: several tens of kHz), is often generated by using radio frequency of 13.56 MHz. Yet, the relationship between the plasma and its driving frequency has seldom been investigated. Hence, in this study, dependence of the atmospheric pressure corona plasma characteristics on the driving frequency was explored experimentally from LF to rf (5 kHz-13.56 MHz). The plasmas generated by the driving frequency under 2 MHz were cylindrical shape of several tens of millimeters long while the 13.56 MHz plasma is spherical and a few millimeters long. As the driving frequency was increased, the plasma length became shortened. At the lower driving frequencies (below 2 MHz), the plasmas existed as positive streamer and negative glow for each half period of the applied voltage, but the discharge was more continuous in time for the 13.56 MHz plasma. It was inferred from the measured I-V curves that the higher driving frequency induced higher discharge currents, and the gas temperature was increased as the driving frequency was increased.