固体介质材料二次电子发射动态特性及抑制方法研究

With the development of high power microwave (HPM) technology, its applied voltage and transmitted power is increasing fast and the equipment size is aimed to be miniaturized, dielectric windows are suffered with high gradient electric field, resulting in phenomena of surface flashover, which has been one of major bottlenecks of future application of HPM. Secondary electron emission plays a dominant role in the formation of surface flashover. This project is focused on dynamic evolution of secondary electron emission, trapped charge accumulation and transport in solid dielectrics. Firstly, secondary electron emission yields and surface charge distribution of typical HPM dielectrics are measured experimentally, and dynamic characteristics of secondary electron emission and charge accumulation are investigated. Subsequently, based on electron scattering model and transport theory, current continuity equations are established to study the whole mechanism of electron/hole traps including production, transfer, spread and recombination, for the aim of clarifying the relationship between external electrons emission, accumulation and bipolar transport of internal electron/hole traps. Finally, influences of different surface modification methods on the suppression of secondary electrons are investigated, compared with different suppression efficiency, to propose the optimized modification method for practical application. This project is helpful to further understanding of electron emission mechanism and seek out available suppression methods, which is significant to promote future development of HPM technology.

近年来高功率微波技术不断发展，由于电压等级和传输功率不断提高以及设备小型化发展的驱动，介质窗表面易发生闪络放电导致微波截止，而介质表面的二次电子发射是其根本原因，成为限制高功率微波技术进一步发展的瓶颈之一。本项目针对固体介质材料的二次电子发射动态特性、电荷积聚特性以及电荷输运等基础问题展开研究。首先通过实验测量典型介质窗材料的二次电子发射系数及表面带电分布，获得二次电子发射动态特性及电荷积聚过程。进而基于电子散射和电荷输运理论，建立电荷连续性方程，研究电子/空穴产生、迁移、扩散和复合等动态过程，揭示材料表面电子发射和电荷积聚与内部电子/空穴双极性输运的内在物理关系。最后实验研究微槽结构、氟化等处理工艺对二次电子发射过程的影响规律，对比抑制效果，提出优化的适合工程应用的方法。本研究可深化二次电子发射物理机制，探索提高闪络阈值的有效技术，对推动高功率微波技术的发展具有重要意义。

固体介质二次电子发射特性是影响真空沿面闪络的关键参数，分析其物理机制及其抑制方法对认识放电发展过程、提升功率阈值具有重要的理论和工程研究意义。本项目围绕着二次电子发射特性的基础模型、仿真模拟、实验测量、抑制策略等方面开展研究。首先，基于电子枪脉冲调制、双层电子收集结构优化等方法，搭建并完善了二次电子发射系数和表面电位联合测量试验平台，获得了典型脉冲功率用介质材料二次电子发射系数及能谱。进而，基于蒙特卡洛数值模拟建立了入射电子散射碰撞模型，分析了电子在固体中散射轨迹和内二次电子产生、输运的动态过程，探讨了电子在材料内部的能量损失机制。研究了二次电子发射及表面电荷积聚动态演化规律，分析了二次电子发射自洽平衡物理机制。基于周期性表面复杂微结构和表面氟化改性方法，获得了表面抑制方法对二次电子发射的影响规律。最后，建立了真空沿面闪络理论模型，提出了综合考虑二次电子发射系数和表面气体解吸附的闪络阈值公式。本研究深化了对二次电子发射物理机制认识，提出了抑制二次电子发射的有效方法，可用于指导相关领域固体介质的表征评价、改性优化和新材料开发，以提升材料的耐电性能和功率密度阈值。