Plasma Jets with Needle-Ring Electrodes: The Insulated Sealing of the Needle and its Effect on the Plasma Characteristics

In this paper, in order to obtain an atmospheric-pressure plasma jet with high activity and safe performance, the plasma jets generated with three distinct needle-ring electrodes, i.e., completely covered needle with insulating dielectric, partially covered needle (PCN) with insulating dielectric, and noncovered needle with any insulating dielectric, are studied and compared. Corresponding characteristics of three types of plasma jets are diagnosed and compared under the same excitation conditions. The results show that the PCN electrode is the best optimized one of three electrodes and presents the best cost performance among them in terms of discharge morphology, safety performance, propagation speed, and concentration of reactive species. It is mainly attributed to the addition of the partial insulating dielectric between the needle electrode and the ring electrode, which would not only effectively limit current rapid growth and prevent the rapid transformation of discharge mode, but also promote the charge overflow and strengthen the chemical activity of the plasma jet.