A Modified Steady-State Method for Space Charge-Limited Effect of SGEMP

Chen, Jinghui; Zeng, Chao; Jianhong, Deng; Li, Zheng-Di

doi:10.1109/tns.2020.3030417

Cited by 10 publications

(5 citation statements)

References 17 publications

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“…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.…”

Section: 为了降低实验复杂性与成本 Sgemp的实验unclassified

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

Zhang¹,

Zhou²,

Zhou³

et al. 2022

Acta Phys. Sin.

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The surface of metal system exposed to ionizing radiation (X-ray and γ-ray) will emit high-energy electrons through the photoelectric effect and other processes. The transient electromagnetic field generated by the high-speed electron flow is called system generated electromagnetic pulse (SGEMP), which is difficult to shield effectively. An ongoing effort has been made to investigate the SGEMP response in vacuum by numerical simulation. However, the systems are usually operated in a gaseous environment. The objective of this paper is to investigate the effect of low-pressure air on the SGEMP. A three-dimensional hybrid simulation model is developed to calculate the characteristics of the electron beam induced air plasma and its interaction with the electromagnetic field. In the hybrid model, the high-energy photoelectrons are modelled as macroparticles, and secondary electrons are treaed as fluid for a balance between efficiency and accuracy. A cylindrical cavity with an inner diameter of 100 mm and a length of 50 mm is used. The photoelectrons are emitted from one end of the cavity and are assumed to be monoenergetic (20 keV). The photoelectron pulse follows a sine-squared distribution with a peak current density of 10 A/cm<sup>2</sup>, and its full width at half maximum is 2 ns. The results show that the number density of the secondary electrons near the photoelectron emission surface and its axial gradient increase as air pressure increases. The electron number density in the middle of the cavity shows a peak value at 20 Torr (1 Torr = 133 Pa). The electron temperature decreases monotonically with the increase in pressure. The low-pressure air plasma in the cavity prevents the space charge layer from being generated. The peak value of the electric field is an order of magnitude lower than that in vacuum, and the pulse width is also significantly reduced. The emission characteristic of the photoelectrons determines the peak value of the current response. The current reaching the end of the cavity surface first increases and then decreases with pressure increasing. The plasma return current can suppress the rising rate of the total current and extend the duration of current responses. Finally, to validate the established hybrid simulation model, the calculated magnetic field is compared with that from the benchmark experiments. This paper helps to achieve a better prediction of the SGEMP response in a gaseous environment. Compared with the particle-in-cell Monte Carlo collision method, the hybrid model adopted can greatly reduce the computational cost.

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Section: 为了降低实验复杂性与成本 Sgemp的实验unclassified

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

Zhang¹,

Zhou²,

Zhou³

et al. 2022

Acta Phys. Sin.

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“…X射线与固体介质相互作用并发射光电子的过程比较复杂 [31] . 本文主要研究二次电子对SGEMP的影响, 因此对端面产生的光电子进行简化处理, 假设其均为单能电子(能量 E 0 ), 运动方向垂直于受辐照面向外 [14,17] , 光电子发射面的电流密度J emi (正比于X射线功率密度与光电产率)在时间上表现为单个脉冲且该脉冲服从正弦平方分布 [13] , 如(7)式所示:…”

Section: 图2为本文涉及的两种典型sgemp计算模unclassified

“…场的振荡 [32] .电荷累积并形成空间电荷层需要一定时间, 对于腔体外SGEMP, 在空间电荷层形成前, 不会有光电子返回金属表面, 也就不会产生二次电子, 所以图4中最初一段时间内考虑二次电子发射不会对电场结果产生影响. 定义电子首次返回发射面的时刻(也即二次电子产生的时刻)为空间电荷层产生的特征时间, 光电子能量越高、电流密度越小, 特征时间越长 [14] .…”

Section: 图2为本文涉及的两种典型sgemp计算模unclassified

“…北京应用物理与计算数学研究所孙会芳等 [13] 使用三维PIC方法计算真空中圆柱腔体的SGEMP. 西北核技术研究院的Chen等 [14] 系统地研究了初级电子能谱等对空间电荷层形成特征时间的影响. 中物院应用电子学研究所的 Chen等 [15] 提出了一种描述SGEMP空间电荷层的方法, 可以有效降低PIC模拟所需计算资源.…”

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Effect of secondary electrons on SGEMP response

Zhang¹,

Zhou²,

Zhou³

et al. 2021

Acta Phys. Sin.

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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.

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“…为了降低实验复杂性与成本， SGEMP 的实验研究往往通过直接注入高能电子束来模拟光电子，避免使用大型射线源，即便如此，相关实验的难度依然很高，公开的实验数据也非常稀缺 [4]- [6] .因此，数值模拟已经成为研究 SGEMP 的重要手段，代表性成果是美国 Woods 等人 [7] 编制的二维模拟程序 ABORC.以往的研究中，真空环境下的 SGEMP 一直是关注的重点 [8] .近五年左右，西北核技术研究所的 Wang 等人基于自研程序 UNIPIC-3D [9] [10] 对 SGEMP 进行模拟，该程序支持辛算法以及共形网格 [11] ，可以有效处理系统电磁脉冲中的电子发射边界问题 [12] .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.实验结果表明 [17] ，等离子体与电磁场的相互作用会使 SGEMP 的特性会发生显著变化.Woods 等人 [18] 最早通过数值模拟研究了高空稀薄空气和预电离空气对 SGEMP 的影响，结果表明，随着气压升高，空间电荷层被破坏，系统表面电流增加 [19] .Chan 等人 [20] 与 Strasburg 等人 [21] 使用电导率模型描述稀薄空气等离子体.Pusateri 等人 [22] 基于 swarm 模型对高空核爆电磁脉冲中的二次电子进行建模.Angus 等人 [23] 建立了零维反应动力学模型，研究电子束诱导稀薄空气等离子体中的主要反应.…”

Section: 引言unclassified

Hybrid Modelling of Cavity SGEMP in Low Pressure Air

中国工程物理研究院研究生院¹,

北京应用物理与计算数学研究所²

2021

Acta Physica Sinica

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A Modified Steady-State Method for Space Charge-Limited Effect of SGEMP

Cited by 10 publications

References 17 publications

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

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

Effect of secondary electrons on SGEMP response

Hybrid Modelling of Cavity SGEMP in Low Pressure Air

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