Simulations of the cathode falling characteristics and its influence factors in atmospheric pressure dielectric barrier glow discharge pulse

Abstract

A fluid model is built in this paper to describe and study the atmospheric pressure dielectric barrier glow discharge pulse in helium. The collision excitation and ionization reactions between electron and helium atom, heavy particles reactions, and Penning reaction between N2 and metastable He are taken into account in the fluid model. It is found that there are cathode falling, negative glow, Faraday dark, positive column and anode glow areas in atmospheric pressure glow discharge pulse, and the ranges of different areas are changing during the current falling edge. The ranges of cathode falling area are defined according to electron production balance position (definition 1, set as dc1) and the electrical field distribution around cathode (definition 2, set as dc2), respectively. Both dc1 and dc2 decreaseas the current grows to its peak in one discharge pulse, which reflects the transition from Townsend discharge to glow discharge. Compared with negative glow peak position, the boundary of cathode falling area by definition 1 is closer to cathode. However, the dc1 cannot reflect the cathode potential falling value and lose its definition after current peak moment. The dc2 can reflect the cathode potential falling value but it causes the overlapping between cathode falling and negative glow areas. At the current peak moment, the glow peak is located at the boundary of cathode falling area according to definition 2 while the glow peak is always located in the cathode falling area during the current falling edge. The cathode falling area characteristics can be influenced by different factors, e. g. applied voltage, secondary electron emission coefficient γ and N2 content. By changing applied voltage, it is found that the electrical potential dropping in cathode falling area increases as the average current density decreases, which indicates that the atmospheric pressure dielectric barrier glow discharge pulse is a subnormal glow discharge, and it is close to the normal glow discharge region. When γ dc1 and dc2 increase sharply with γ decreasing. When γ >0.02, dc1 and dc2 increase slowly with γ increasing. When N2 content is greater than 4 ppm, dc1 and dc2 first decrease and then increase slowly. The electrical potential falling of cathode is changeless with N2 content changing. However, the voltage across the gas gap decreases with N2 content changing because the Penning effect lowers the breakdown voltage of the gas gap. The spatial average current density has a highest value when N2 content is about 35 ppm, which also means that the spatial average charged particle density has the highest value in the same situation. Moreover, when the secondary electron emission coefficient is a constant, both dc1 and dc2 have negative linear relationship with the average current density.