Effect of secondary electrons on SGEMP response

Abstract

It is difficult to effectively shield the system generated electromagnetic pulse (SGEMP), which can significantly affect the performance of important electronic devices and infrastructure, such as low-orbit spacecraft. Numerical simulation is an essential way to study the SGEMP response. However, many previous studies ignored or simplified the effect of secondary electron emission in their models. In this paper, a three-dimensional electromagnetic particle-in-cell numerical simulation model is developed to evaluate the effect of secondary electrons on the SGEMP response of two typical structures (external SGEMP and cavity SGEMP, respectively) under different current densities (0.1–100 A/cm<sup>2</sup>) and different materials (Al, Cu and Au). A right cylinder or cylindrical cavity with a length of 100 mm is used. The photoelectrons produced by the interaction between the X-ray photon and metal are emitted from one end of the system and assumed to be monoenergetic. The photoelectron pulse follows a sine-squared distribution, and its full width at half maximum is 1 ns. Some important parameters of secondary electrons are discussed and summarized, including the emission coefficients of elastically and inelastically backscattered electrons, as well as the probability density functions of emission angles and energies. The results show that ignoring the secondary emission in the simulation model leads the peak electric field to be underestimated by twice-thrice, and the duration of electric field response by more than 10%. The oscillation frequency and the amplitude of the second peak of the tangential magnetic field are also increased, with the secondary electrons considered. Among various types of secondary electrons, backscattered electrons have a dominant effect on the change of SGEMP. The effect of true secondary electrons is about 1/5 of that of backscattered electrons. The effect of secondary electrons on SGEMP response increases with a higher atomic number of the material used in the system, mainly due to higher backscattering emission coefficient and a high ratio of high energy inelastically backscattered electrons. The secondary electrons will influence the response of the external SGEMP only when the space charge effect is strong (high X-ray fluence). While the response of the cavity SGEMP is more easily affected by the secondary electrons even at a relatively low X-ray fluence. This paper helps to better obtain the SGEMP response of a specific device under strong radiation through numerical simulation.

Hybrid modelling of cavity system generated electromagnetic pulse in low pressure air

“…近五年左右, 西北核技术研 究所的Wang等 [9−12] 基于自研程序UNIPIC-3D 对SGEMP进行模拟, 该程序支持辛算法以及共 形网格, 可以有效地处理系统电磁脉冲中的电子发 射边界问题. 国内研究人员对其中存在的空间电荷 限制效应 [13,14] 、壁面二次电子发射 [15] 等问题也进 行了广泛的研究 [16] . 然而, 实际系统往往工作在气体环境或含有充 气元器件, 光电子与中性气体间会通过碰撞电离产 生大量的次级电子、离子对, 次级电子又会从电磁 场中获得能量, 继续与中性气体发生电离、激发等 一系列反应, 从而形成等离子体.…”