Development of a non-equilibrium 60 MHz plasma jet with a long discharge plume

Abstract

High-frequency plasma jets driven by voltages in the frequency range of 6–60 MHz are developed. A long plasma jet, 40 mm in length, is successfully produced by using a pair of ring electrodes outside a quartz tube. The electrode pair consists of a wide power electrode and a narrow ground electrode that is positioned at the head of the tube. The ratio of the length of the ground electrode to the length of the power electrode must be small in order to produce long plasma jets. The high-frequency plasma jet is operated in a non-thermal-equilibrium state at a gas temperature of around 60 °C. Operation at the very-high-frequency of 60 MHz leads to a lower discharge voltage and lower electron energy compared to lower frequencies of 6 and 13.56 MHz. The ability of the very-high-frequency (60 MHz) plasma jet to produce reactive oxygen and nitrogen species in water is also investigated. High H2O2 and NO3− concentrations of more than 1 mmol/l are realized by irradiating 3 ml of deionized water with the plasma for a short period of 2 min.