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

Abstract

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.