高能电子辐射下聚四氟乙烯深层充电特性

介质深层充放电现象是诱发航天器异常故障的重要因素之一.分析了高能电子辐射下介质内部电荷沉积、能量沉积特性和电导特性,考虑了真空与介质界面电荷对电场分布的影响,建立了介质二维深层充电的物理模型,并基于有限元方法实现了数值计算.计算了高能电子辐射下聚四氟乙烯的深层充电特性.结果表明:真空环境下,介质的表面存在较弱的反向电场,随着介质深度增大,电场减小至零,随后逐渐增大,最大值出现在靠近接地附近,但在接地点,电场存在小幅降低.分析了不同辐射时间下(1 h,1 d,10 d和30 d),介质内部最大电位和最大电场的时空演变特性.随着辐射时间的增加,最大电位由-128V增加至-7.9×104V,最大电场由2.83×105V·m-1增加至1.76×108V·m-1.讨论了入射电子束流密度对最大电场的影响,典型空间电子环境(1×10-10A·m-2)下,电子辐照10 d时,介质内部最大电场为2.95×106V·m-1.而恶劣空间电子环境(2×10-8A·m-2)下,电子辐射42 h,介质内部最大电场即达到108V·m-1,超过材料击穿阈值(约为108V·m-1),极易发生放电现象.该物理模型和数值方法可以作为航天器复杂部件多维电场仿真的研究基础.

Research of deep dielectric charging characteristics of polytetrafluoroethene irradiated by energetic electrons

Deep-layer dielectric charge and discharge in insulating material irradiated by energetic electrons are one of the major factors causing spacecraft anomalies. In this paper we establish a two-dimensional physical model of deep-layer dielectric charging, based on charge distribution and energy deposition of incident electrons and conductivity properties. The model is accomplished by finite element method, and the deep-layer dielectric charging characteristics of polytetrafluoroethene irradiated by energetic electrons are calculated. The calculation results show that in the vacuum environment, in the surface of the dielectric there exists a weak reverse electric field, and it first decreases to zero and then increases with the increase of depth. The maximum electric field appears near the ground, but the electric field presents a slight reduction at the position of ground point. Space-time evolution characteristics of the maximum potential and maximum electric field in different radiation times (one hour, one day, ten days and 30 days) within dielectric are analyzed. With the increase of radiation time, the maximum potential increases from -128 V to -7.9× 10⁴ V, and the maximum electric field increases from 2.83×10⁵ V·m^-1 to 1.76×10⁸ V·m^-1. Finally, the influence of electron-beam density on the maximum electric field is discussed. In a typical space environment (1×10^-10 A·m^-2), the maximum electric field reaches 2.95×10⁶ V/m·m^-1 for ten days. However, in severe space environment (2×10^-8 A·m^-2, the maximum electric field rapidly reaches 10⁸ V/m for 42 hours, exceeding the breakdown threshold (about 10⁸ V·m^-1), which may easily cause electrostatic discharge). The physical model and numerical method can be used as a research basis of multi-dimension electric filed simulation of spacecraft complex parts.
Keywords： deep dielectric charging polytetrafluoroethene energetic electrons radiation two dimension electric field simulation