Pulsed Atmospheric-Pressure DBD Plasma Produced in Small-Diameter Tubes

This paper presents the experimental results on the characterization of plasma produced in narrow tubes using a pulsed dielectric barrier discharge (DBD), working in helium or helium-oxygen gas mixture at atmospheric pressure, in a symmetrical configuration of external electrodes. This paper focuses on the effect induced by the total gas flow rate and gas composition on the characteristics of pulsed DBD. Using tunable diode laser absorption spectroscopy, ultraviolet absorption, and optical emission spectroscopy, complementary information on the reactive species (O, O₃, N₂, and N₂⁺ ) present in the discharge has been obtained. It results that the excited species generated by direct electron excitation (as He and N₂) follow the evolution of their precursors with increasing gas flow rate, while those created by chain reactions (as N₂⁺ , O, and O₃) depend on the collective behavior of all their precursors, regardless of the fact that these are originating from the feeding gas or are coming from impurities. At specific energies, between 5 and 50 J/L, and a gas temperature of 315 ± 20 K, the atmospheric-pressure plasma is able to produce 10¹⁴-10¹⁵ m^-3 of O (3⁵S₂) or (1.5-2.8) × 10¹⁵ cm^-3 of O₃, depending on the feeding gas composition and its flow rate. Low gas temperature and high density of reactive species could make the present DBD arrangement suitable for medical applications.