Spatiotemporal characteristics of sheath of microwave argon plasma at intermediate pressure

Abstract:

The properties of the sheath directly affect the quality of microwave plasma applied to industry and other fields. Aiming at the difficulty in studying the time-varying spatial distribution and electric field distribution, the finite element method was used to establish a microwave-argon plasma three-dimensional model coupled with Maxwell's equation at medium pressure to analyze the spatiotemporal characteristics of the sheath and give its two-dimensional equivalent model. Based on the analysis of the parameters of plasma, the formation process of the sheath and the change trend of its thickness were presented. The time-space transient characteristics of the plasma electric field and the microwave electric field were compared respectively. The results show that in time, due to the different diffusion speed and stress direction of electrons and ions the thickness of the sheath increases gradually, and eventually forms a steady state sheath; In space, the sheath exists near all the discharge tube walls adjacent to the plasma. The electric field intensity of the sheath layer is always greater than that of the bulk plasma region, and the direction of the electric field always points to the tube wall, which has a damping effect on the microwave electric field. In addition, it is proved by quantitative analysis that the thickness of sheath decreases with the increase of pressure.