Formation and destruction of striation plasmas in helium glow discharge at medium pressures

The striation plasmas are usually generated in positive column of glow discharge, in which abundant and complex physics are involved, especially, in medium or high pressures. This paper was aimed at investigating the formation and deformation of helium striation plasmas at kPa level pressures. The characteristics of helium striation plasmas, especially, the optical emission characteristics were investigated. The emission lines of 706.52 nm and 391.44 nm related to energetic electrons and high energy metastable helium atoms were focused on during the discharge process. Formation of striation plasmas in helium glow discharge, is mainly associated with the instability resulting from stepwise ionization vis high energy metastable state atoms, Maxwellization of electron distribution functions and gas heating. The deformation effect of helium striation plasmas is very significant when a small amount of nitrogen or oxygen is mixed into the discharge plasmas. The reduction of mean electron energy and the consumption of high energy metastable helium atoms are the potential reasons for deformation of striation plasmas.

The Ag+ Reduction Process in a Plasma Electrochemical System Tuned by the pH Value

The interactions between discharge plasmas and an aqueous solutions can enable the production of reactive species and charge transfer at the plasma-liquid interface, forming the plasma electrochemical system (PES). The PES are promising for diverse applications, such as nanomaterials synthesis, due to the activation of the solution chemistry by the plasma. In this paper, we investigate the influence of the solution’s pH value on the formation of silver nanoparticles (AgNPs) in a direct current (DC) PES. Dual argon DC plasmas are generated in an H-type electrochemical cell containing an aqueous solution of silver nitrate with pH values in the range of 1.99-10.71. By this design, the solution acts as a cathode at one end of the H-type cell, and as an anode at the other end. The results show that the AgNPs are formed at the anode except for the solution with the pH value of 1.99. However, at the cathode, the AgNPs only appear in the solution with the pH value of 10.71. We find that the solvated electrons and hydrogen peroxide produced by the plasma-liquid interactions are responsible for the Ag+ reduction at the solution anode and the solution cathode, respectively.

15th International Conference “Gas Discharge Plasmas and Their Applications”

This paper is a preface to the proceedings of the 15th International Conference “Gas Discharge Plasmas and Their Applications”, which was held in Ekaterinburg, Russian Federation on September 5 to 10, 2021.