空间电荷和介质表面电荷对微放电演化过程的影响

Impacts of space and dielectric surface charges on evolution of multipactors

微放电是制约航天器微波部件功率容量的主要瓶颈之一。以介质微波部件中典型的介质加载平行板波导为例,基于三维粒子模拟分别对仅考虑外加微波场(情况1)、考虑外加微波场和空间电荷(情况2)以及考虑外加微波场、空间电荷和介质表面电荷(情况3)三种情况下微放电演化过程中电子数目、瞬态二次电子发射系数、归一化反射波电压以及介质表面与上金属板之间的间隙电压随时间的变化进行了仿真,并给出了情况3电子分布和介质表面电荷密度随时间的变化过程。在此基础上,明确了空间电荷和介质表面电荷在微放电过程中所起的不同作用:即空间电荷会使微放电达到饱和状态,介质表面电荷则导致微放电饱和状态无法持续,最后自行熄灭。介质表面电荷导致了微放电过程中介质和金属瞬态二次电子发射系数下降速率不一致,归一化反射波电压幅度随时间变化的包络类似于“眼睛”形状、间隙电压类直流偏置、非对称电子能量分布等特殊现象。

Multipactor is one of the bottlenecks for spaceborne high-power microwave components.In this work,based on 3D particle-in-cell simulation,we investigate the fluctuation of number of electrons,the instantaneous secondary electron yield,the normalized reflection wave voltage and the gap voltage between the dielectric surface and metallic plate in the evolution of multipactors with parallel-plate dielectric-loaded waveguide for three cases:just considering external microwave field(case 1),considering both external microwave field and space charge(case 2),and considering external microwave field,space charge and surface charge on the dielectric(case 3).The electron distribution and charge density on the surface of dielectric versus time for case 3 are given.Simulation results reveal the roles of space charge and surface charge on the dielectric:space charge results in the saturation state of the multipactor,while surface charge on the dielectric results in an unsustainability of the saturation,extinguishing the multipactor.The existence of surface charge on the dielectric is responsible for the special circumstances including the different decreasing rate of instantaneous secondary electron yield of dielectric and metal plate,the eye-like shape of envelope of the normalized reflective wave voltage amplitude,the gap-voltage DC-like bias,and the unsymmetrical distribution of the energy of electrons.