Discussion on the influences of townsend ionization coefficient α and secondary electron emission coefficient γ on the characteristics of DBD
Dielectric barrier discharge (DBD) has drawn great attentions in recent years, and the discharge physic is one of the research focuses. In this paper, both Townsend ionization coefficient α and secondary electron emission coefficient γ (SEEC) in DBD are discussed. The value and partial derivative of α in pure helium are compared with that of argon theoretically, which is related to the breakdown voltage and discharge channel radius. The changes of discharge channel radius under different electrical field is obtained, and the high nonlinear relationship between α and electrical field (∂(α)/∂(E)) is believed to be the main reason for discharge contraction. Therefore, we mix a little NH3 in argon to make the α different from that of pure argon and work in the region where the ∂(α/∂(E) is relatively low. In this way, the uniform discharge, similar with He-DBD, can be obtained in the Ar/NH3 DBD.The SEEC y of dielectric is another important parameter in gas discharge. Different types of Townsend discharge is achieved, the value range of y in various dielectrics is estimated based on y(eαd-1) ≈1. The y in He-DBD and N2-DBD is studied and compared to clarify the gas species' effects on y as well. The electron trap feature of dielectric surface and gas species energy are used to explain the changes of y. Moreover, the cathode falling thickness of different dielectric surface is measured according to the luminous structure when DBD is in glow-like discharge region, which may be affected by γ.