基于二维PIC-DSMC耦合算法的真空沿面闪络形成过程的等离子体演化特性

Plasma Evolution of Surface Flashover Form Process in Vacuum by 2D PIC-DSMC Code

真空沿面闪络一直是限制相关高压技术应用的重要问题,因此通过深入认识真空沿面闪络形成过程等离子体演化特性来掌握影响等离子体形成和演变的主要因素,对进一步提高相关器件耐压性能有重要意义。为此基于金属-真空-绝缘体交界处的三相点场致电子发射、绝缘体表面电荷累积、二次电子发射、气体解吸附及电子与解吸附气体相互作用等基本物理过程,通过二维轴对称PIC-DSMC（网格质点法-直接模拟蒙特卡罗法）耦合算法建立了1 mm间隙的真空沿面闪络仿真模型,阐明了电子、离子和中性粒子的时空分布演化特性,揭示了绝缘体表面电荷累积对阴极表面电场的增强作用以及其导致的三相点场致发射电子增加,阐明了阴极附近正离子大量出现并增强场致发射导致了阴极附近首先形成电子雪崩并从而引起真空沿面闪络的物理过程,从而获得了完整的真空沿面闪络形成过程中的等离子体演化特性,这为深入理解真空沿面闪络机制和进一步提高相关器件性能奠定了基础。

The surface flashover is a major limitation to high-voltage components in vacuum, therefore it is important to master the main factors which affect the plasma formation and evolution in surface flashover for further enhancing the insulating performances of relative components. We established a simulation model of the surface flashover in 1 mm vacuum gap by a 2 D PIC-DSMC code, in which some basic physical processes, such as field emission in the vicinity of the metal-vacuum-dielectric junction, charge accumulation effect in insulator surface, secondary electron emission, gas desorption, and electrons interact with gas etc, were considered. Then, the temporal and spacial density distribution of electrons, ions and neutral particles are presented. The enhancement of electric field on cathode surface and the increases of field emission electrons induced by the charge accumulation effect on insulator surface is revealed. Finally, it is indicated that surface flashover is formed as massive ions appearing near the cathode to enhance field emission. The results provide a base for further understanding the surface flashover in vacuum and further enhancing the performances of components.