Realization of homogeneous dielectric barrier discharge in atmospheric pressure argon and the effect of beads on its characteristics

This paper describes the realization of a homogeneous dielectric barrier discharge (DBD) in argon at atmospheric pressure. The effect of the morphology of the dielectric surface (especially the dielectric surface covered by hollow ceramic beads (99% Al2O3) with different diameters) on discharge is investigated. With different dielectrics, the argon DBD presents two discharge modes: a filamentary mode and a homogeneous mode. Fast photography shows that the filamentary mode operates in a streamer discharge, and the homogeneous mode operates in a Townsend discharge regime. It is found that a homogeneous discharge can be generated within a certain voltage range. The voltage amplitude range decreases, and the breakdown voltage increases with the increase in the mean diameter of the ceramic beads. Waveforms of the total current and optical emission signal present stochastic pulses per half voltage cycle for the filamentary mode, whereas there is one single hump per half voltage cycle for the homogeneous mode. In the homogeneous mode, the intensity of the optical emission decreases with the mean diameter of the ceramic beads. The optical emission spectrum is mainly composed of atomic lines of argon and the second positive system of molecular nitrogen. It reveals that the electron density decreases with the increasing mean diameter of the ceramic beads. The vibrational temperature increases with the increasing mean diameter of the ceramic beads. It is believed that a large number of microdischarges are formed, and smaller ceramic beads have a larger activation surface area and more point discharge. Electrons liberated in the shallow well and electrons generated from microdischarges can increase the secondary electron emission coefficient of the cathode and provide initial electrons for discharge continuously. Therefore, the breakdown electric field is reduced, which contributes to easier generation of homogeneous discharge. This is confirmed by the simulation results.