电子束辐射下聚四氟乙烯的电荷输运特性与机理研究

The interaction of charged particles, such as electrons, protons, and ions, and insulation material on spacecraft will cause charge deposition, ionization, excitation, and coulomb collision in the material. Irradiation induced deep dielectric charging/discharging (DDCD) of the insulation material in space environment extremely affects the safe operation and life time of spacecraft. The charge transport properties of insulating material determines the DDCD physical processes, including charge deposition and dispersion. Nevertheless, the charge transport properties of Polytetrafluoroethylene (PTFE) which is widely used in space field, such as conduction mechanism, charge injection from electrode to insulating material, and the formation and transportation of charge packets, are not very clear until now. This project will investigate the charge transport properties and mechanisms of PTFE under various temperatures, various electric fields and various charge concentration gradients. We will study the surface potential decay curves by Runge-Kutta Discontinuous Galerkin method (RKDG) and Boundary Element method (BEM) to derive the conduction properties of the material. The trap energy and density of the material will be revealed by dielectric space charge mapping techniques (Pulsed Electro-Acoustic), thermal simulated current (TSC), and dielectric spectroscopy. Based on the experimental results, we will research the charge trapping and detrapping mechanism, and charge pairs generation and recombination of the dielectric material by bipolar charge transport model (BCT). After obtained the charge transport properties of PTFE, the DDCD of the material will be investigated by BCT model by considering charge and energy deposition in dielectric under electron irradiation. The project can provide theoretical fundamentals and experimental results for the development of novel deep dielectric charging and discharging mitigation methods.

空间中电子束或离子束与航天器介质材料相互作用时，会造成介质中的电荷捕获、电离、激发等物理过程,进而造成介质的深层充放电现象，极大地影响着航天器的安全运行和寿命。介质的电荷输运特性决定着电子束辐射下介质的深层电荷沉积和消散等充放电物理过程，然而航天领域广泛应用的聚四氟乙烯的电荷输运特性和机制尚不完全清楚。本项目围绕电子束辐射下介质充放电物理过程，研究温度场、电场和电荷浓度梯度场耦合作用下聚四氟乙烯的电荷输运特性和机制。采用龙格-库塔间断伽辽金方法分析介质的表面电位衰减曲线，提取其电导特性；采用空间电荷测量方法、热刺激电流和介电谱等研究材料的陷阱分布；结合双极性电荷输运模型（BCT）研究电荷入陷、出陷机理和电子空穴对的产生与复合机制。进而考虑电子辐射下介质中的电荷分布与能量沉积，采用BCT模型弄清电子束辐射下介质的深层充放电物理过程，为介质深层充放电新防护理论和方法提供理论基础和实验依据。

航天用介质材料的深层带电特性严重威胁航天器的安全运行。电子束辐射下聚四氟乙烯的电荷输运特性决定了聚四氟乙烯的介质深层带电特性，同时也影响其放电过程。本项目采用热刺激电流和等温表面电位衰减等方法提取了材料的陷阱分布特性，研究了温度场、电场和电荷浓度梯度场耦合作用下聚四氟乙烯的电荷输运特性和机制，测量了聚四氟乙烯的二次电子发射特性。考虑电极/介质界面的电场和电荷密度、电介质中载流子的迁移与扩散、以及电介质中的陷阱，建立了电极/电介质间的自适应电荷注入模型。在电子束辐射下，考虑了电子在聚四氟乙烯内部的电荷沉积和能量沉积过程，辐射区域采用了辐射诱导电导，建立了电子束辐射下的电荷注入模型。使用电荷连续性方程、电流传导方程和泊松方程描述电介质中的电荷输运过程。研究了电荷入陷、出陷机理和电子空穴对的产生与复合机制。考虑电子束辐射下聚四氟乙烯的二次电子发射特性和表层电荷输运特性，以及电子辐射下介质中的电荷分布与能量沉积，采用电荷输运模型研究了电子束辐射下介质的深层充放电物理过程。分析了电子束能量、试样厚度、温度、陷阱密度等因素对电子束辐射下聚四氟乙烯材料的电荷输运特性的影响。建立了高能电子辐射下聚四氟乙烯的一维和二维空间电荷输运模型，研究了高能电子辐射下介质内部的电荷、电位、电场分布特性。空间电荷输运模型可用于电子束辐射环境下绝缘介质的内带电风险的预测，对航天器充放电效应领域具有重要的意义。