微波输出窗内表面闪络击穿3维全电磁等离子体流体模拟

3Dfully electromagnetic field and plasma fluid simulation of inner surface flashover and breakdown on microwave window

通过建立电磁场等离子体流体耦合物理模型,基于自主研发的3维全电磁粒子模拟大规模并行程序NEPTUNE3D,编制了3维电磁场与等离子流体耦合程序模块,对1.3GHz高功率微波窗内表面闪络击穿物理过程进行了数值模拟。研究结果表明:微波窗内侧表面形成的等离子体构型与初始种子电子分布形式密切相关。中心点源分布下,等离子体发展为"蘑菇"形状,输出微波脉冲缩短并不严重,等离子体吸收微波功率大于反射微波功率;面源分布下,等离子体发展为"帽子"形状,输出微波脉冲缩短严重,输出微波完全截断,开始阶段等离子体吸收微波功率占优,待等离子体密度增加到一定程度后,反射微波功率占优。通过降低窗体表面场强、表面释气率及初始种子电子密度等方法,可不同程度地延长输出微波脉冲宽度。窗体表面不同气体层厚度对闪络击穿下的输出微波脉冲宽度影响不大。

Based on an independently developed large-scale parallel code NEPTUNE3 D,a module of electromagnetic field finite-difference-time-domain method coupled with a plasma fluid model is programmed and built to investigate the physical phenomena of high power microwave(HPM)flashover and breakdown on the inner surface of the output window.By using improved NEPTUNE3 Dcode,the 1.3GHz HPM flashover and breakdown on the inner surface of the output window are simulated.The numerical results indicate that the plasma shape formed in flashover and breakdown is relevant to the initial seed electron distribution type.For the point source central distribution,the developing plasma configuration is like a mushroom;the shortening of the output microwave caused by plasma absorption is not serious.For the face-source distribution,the developing plasma configuration is like a hat;the shortening of the output microwave is intense,the plasma absorption effect is dominant at the initial stage,while the plasma reflection effect dominates when the plasma density is up to a high enough value.The output microwave pulse width could be prolonged by decreasing the microwave power,the outgassing rate and the initial seed electron density,respectively.The outgassing depth barely affects the width of the shortened microwave output pulse.