在X波段微波源(频率9.4 GHz,功率1 GW)下,对4种典型介质窗材料(聚四氟乙烯、有机玻璃、低密度聚乙烯及高密度聚乙烯)在真空中进行了微波放电击穿实验,同时考虑了材料的不同表面处理工艺(表面刻槽和抛光)对其击穿特性的影响,对微波击穿后样品的表面形貌进行了宏观和微观分析,实验观测到:介质表面出现了沿微波电场方向的明显树枝状破坏现象,且材料表面处理工艺对其击穿破坏程度有显著影响,认为树枝状破坏通道与施加的微波场有着密切的关系。通过观察透明有机玻璃内部的树枝状破坏,发现树枝既沿介质表面生长,同时也向介质内部发展。提出了微波作用下介质窗击穿破坏的物理模型,认为微波电场导致树枝状破坏沿电场方向发展,而微波磁场导致树枝状向介质内部发展,并进一步给出了树枝状破坏起始和发展的可能原因。

The microwave discharge experiments of dielectric window were performed in vacuum under X-band HPM with the frequency of 9.4 GHz and the power of 1 GW. Several typical dielectric window materials,i.e.,PTFE,PMMA,LDPE and HDPE,were employed,and the influence of different surface treatments as notching and polishing was investigated. After microwave breakdown experiments,the surface morphology of dielectric samples were analyzed with the macroscopic and microcosmic view. It was found that there were obvious single-surface tree-like breakage phenomena occurred along the direction of microwave electric field,and the surface destroy status was significantly affected by the different surface treatment. It is considered that the tree-like depredation channels are closely related to the applied microwave field. By observing the tree failure inside the transparent PMMA sample,it was found that,the tree developed along the surface and also to the inner of material. A physical model is proposed to describe the dielectric window breakdown under HPM. It is suggested that the electric field of microwave results in the tree development along the material surface,and the tree develops into the material under magnetic field. Moreover,the possible reasons are revealed to describe the tree initiation and development inside the dielectric window.