We succeeded in putting forward a two-dimensional electric transport model based on the first-order kinetic charge trapping/detrapping model. The dynamic conductivity under thermal cycle of polyimide is analyzed from numerical calculations and experimental tests. The conductivity characteristics of polymer dielectric under temperature cycling was found to be dominated by temperature and time, because of filled traps and rapid changes in temperature. The present study contributes in providing an accurate conductivity calculation model for polymer dielectrics under temperature-varying fields.

Traditionally, conductivity, a key parameter for evaluating the probability of electrostatic discharge, has been subscribed to the belief that it is a constant value. However, in actual working conditions, such as the low earth orbit environment, the conductivity value of dielectrics is not constant due to the variation in temperature. Therefore, it is of great practical significance to investigate the conductivity value of dielectrics in the time-varying field and explore the hidden mechanism of the charging phenomenon. In this paper, we investigated the dynamic conductivity value using polyimide during four temperature cycles. The result shows that there is a positive correlation between conductivity and temperature above the turning point temperature. However, when the temperature is lower than the turning point temperature, the conductivity value hardly changes with temperature. In the four cycles, the conductivity value in the same temperature decreases with the cycles. The space charge distribution test and the thermally stimulated current experiment are carried out to explain the charging phenomenon. The results show that the heterocharge accumulates continually and is captured by deep traps above 0.55 eV. It could be concluded that the thermally stimulated detrapping effect makes the charge trapping difficult, which results in the conductivity value in the same cycle changing with the temperature above the turning point temperature and the heterocharge accumulating. The trap-filling effect inhibits the charge conduction process, which makes the conductivity value in the same temperature to decrease with temperature cycles.

Charge accumulation is one of the main factors leading to electrostatic discharge and restricting the development of spacecraft. This paper investigates the effect of temperature (243-343 K) on the charging behaviour of polyimide in vacuum using electron beam radiation test system. The surface potential distribution shows that there are two charging modes, 'negative-peak' mode and 'negative-crater' mode. For investigating the charge accumulation mechanism, the space charge experiments were carried out by the method of pulsed electro-acoustic. The thresholds of injection from the polyimide/electrode interface are affected by temperature. Under high temperature (above 323 K), the hole could be easily injected from the polyimide/electrode interface, with the extremely low injection threshold. The incident electrons and the injected holes co-existence and form the 'negative-peak' mode. Under low temperature (below 303 K), the area of hole injection from the electrode decreases with the decrease in temperature. The hole injected locally forms an opposing electric field, which makes the surface potential present the 'crater' mode. This work shows that the hole injected from the dielectric/electrode interface play a critical role in the charge accumulation process under electron radiation, which has important significance to avoid the spacecraft electrostatic discharge problem.

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