Repetitive pulsed gas–liquid discharge in different atmospheres: from discharge characteristics to plasma–liquid interactions

Abstract

Gas–liquid discharges enable efficient plasma–liquid interactions and thus have promising applications, but many concerns remain unanswered regarding working gas, an important influencing factor. Investigations of a pulsed needle-to-water gas–liquid discharge in Ar, He, and N₂ are carried out in this study. Voltage–current waveforms and intensified charge-coupled device (ICCD) images were combined to explore discharge modes and evolution processes. Experimental results demonstrate that the Ar tip spark discharge develops all the way to liquid compared with the He and N₂ discharges concentrated in the tube, considerably increasing the plasma–liquid interaction efficiency. According to the optical emission spectra (OES), plasma properties are found to be strongly influenced by interactions between gas particles and interfering particles (H₂O, etc.). For instance, excess water vapor causes quenching of excited species, resulting in OH (A–X) in Ar and NO (A–X) in N₂ concentrated in the middle region with weak discharge. By adding dimethyl sulfoxide, it is demonstrated that OH dominates H₂O₂ production in Ar and contributes to both NO₂⁻ and NO₃⁻ generation in Ar and He, whereas in N₂ it only affects NO₃⁻ generation. This study advances the “bridge building” between practical application and gas–liquid discharge employing different working gases.