基于中压微波氩等离子体的鞘层时空特性研究

Spatiotemporal characteristics of sheath of microwave argon plasma at intermediate pressure

鞘层特性直接影响微波等离子体应用于工业等领域的质量,针对研究其时变的空间分布和电场分布具有一定难度的问题,运用有限元的方法建立了中等气压下耦合麦克斯韦方程的微波氩等离子体三维模型,对鞘层的时空特性进行分析,给出了其二维等效模型.基于对等离子体参数的分析,讨论了鞘层的形成过程及其厚度的变化趋势,对比分析了等离子体电场及微波电场的时空瞬态特征.结果表明:在时间上,由于电子与离子的扩散速度和受力方向不同,鞘层的厚度呈逐渐增大的趋势,并最终形成稳态鞘层;在空间上,鞘层存在于所有与等离子体接触的放电管壁附近,鞘层区域的电场强度始终大于等离子体主体区域,且电场方向始终指向管壁,对微波电场产生阻尼作用.此外,通过量化分析证明了鞘层厚度随压强的增大而逐渐减小.

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.