To study the electromagnetic radiation effect of a thermal control layer (TCL) on the surface of general spacecraft in a space environment, a model of thermal control material irradiated with microwaves was established, a particle-in-cell (PIC)-Monte Carlo collisions (MCC) simulation was used, and the processes of field emission, multipacting, outgassing, and impact ionization on the surface of thermal control materials were simulated. By comparing the primary electrons, secondary electrons, and impact ionization electrons produced under different field intensities and frequencies of electromagnetic waves, different compositions of outgassing, and different thermal control materials, the influencing factors and critical thresholds of avalanche ionization were obtained. The simulation results show that whether avalanche ionization occurs in outgassing on the surface of the TCL is affected by the electromagnetic wave amplitude, electromagnetic wave frequency, outgassing composition, and the material of the TCL. This provides a theoretical reference for the safe operation of spacecraft.
Studying flashover characteristics in vacuum environment is extremely significant for designing reliable insulation structures. The waveform of applied voltage excitations greatly affects the flashover process. In this study, the influence of nanosecond pulse front steepness on flashover process in vacuum is investigated. Firstly, flashover experiments with nanosecond pulses are conducted. Nanosecond pulses with different front steepness are generated and used to trigger flashovers on sample surface. The relationship between pulse front steepness and flashover voltage is studied. Meanwhile, a particle-in-cell with Monte Carlo collision (PIC-MCC) two-dimensional self-sustaining discharge model based on secondary electron emission avalanche (SEEA) scheme is established. The distribution of charged particles, electric field and their evolution during flashover process are presented. Furthermore, pulses with various rising steepness are applied to the model. The multiplication and propagation of charged particles in different pulse waveform conditions are studied. In all conditions, two stages during flashover process can be obviously distinguished based on charged particle number evolution which divides the overall flashover delay time into two parts. By analyzing the voltage development in these two time slots, the quasi-linear relationship between pulse front steepness and flashover voltage in nanosecond pulse flashover in vacuum is explained.
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