Physicochemical properties of the AC-excited helium discharges using a water electrode

In this paper,the AC-excited helium discharges generated between the powered needle electrode enclosed in a conical quartz tube and the grounded de-ionized water electrode are investigated.The current and voltage waveforms exhibit a transition from the glow-like to streamer-like mode discharges,which forms a stable cone-shaped structure at the gas-liquid interface.In this region,the air and water vapor diffusion initiate various physical-chemical processes leading to substantial changes of the primary species emission intensities (e.g.,OH,N2,NO,and O) and the rotational temperatures.The experimentally measured rotational temperature at the gas-liquid interface is 870 K from the N2(C-B) band with a power input of 26 W.With the prolongation of the discharge time,significant changes in the discharge voltage and current,discharge emission patterns,instantaneous concentrations of the secondary species (e.g.,H2O2,NO2-,and NO3-) in the liquid phase,pH values and electrical conductivities of the liquids are observed experimentally.The present study is helpful for deepening the understandings to the basic physical-chemical processes in the discharges in contact with liquids,especially to those occurring in the vicinity of the gas-liquid interface,and also for promoting existing and potential applications of such type of discharges in the fields of environmental protection,biomedicine,agriculture,and so on.