Simulation study of external system generated electromagnetic pulse in low pressure air or plasma
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摘要: 为研究大气环境对系统电磁脉冲（SGEMP ）的影响，针对海拔50～100 km的X射线能量沉积区，分别应用3维PIC程序及3维PIC-MCC程序各自开展预电离等离子体和稀薄空气条件下外SGEMP的建模与模拟研究，针对3种不同的X射线注量（4×10−3 J/cm2、4×10−2 J/cm2、0.4 J/cm2），分别取对应两种不同海拔高度（70 km和80～90 km）的本底等离子体及海拔56 km的稀薄空气条件进行模拟计算，并和真空中的计算结果进行对比，得出预电离等离子体及稀薄空气对外SGEMP的影响规律：当X射线注量较低时，等离子体使得磁场增大，电场减小，而稀薄空气对外SGEMP效应影响不明显；随着X射线注量增大，空间电荷非线性效应越来越明显，等离子体及稀薄空气都使得电场、磁场同时增大，且稀薄空气的增大效应更显著。Abstract: For examining effects of atmosphere on system generated electromagnetic pulse (SGEMP), the external SGEMP are simulated by the 3D PIC code in pre-ionized plasma and by the PIC-MCC code in low pressure air respectively in the X-ray energy deposition region (50 km to 100 km). For three fluences of X-ray (4×10−3 J/cm2、4×10−2 J/cm2、0.4 J/cm2), the simulations are done in pre-ionized plasma corresponding to two different altitudes (70 km and 80−90 km) and low pressure air corresponding to 56 km altitude each other, and the results are compared with those in vacuum. The variation laws of external SGEMP in pre-ionized plasma and low pressure air are received : the effects have relation to fluence of X-ray, when the fluence of X-ray is low, the magnetic field increases and the electric field decreases in the plasma environment, while the variations of external SGEMP are not obvious in low pressure air; with the fluence of X-ray increasing, the space charge nonlinear effects become more and more obvious, the electric field and magnetic field are enhanced together in both pre-ionized plasma and low pressure air, and the enhancement effects are more significant in low pressure air.
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Key words:
- PIC code /
- system generated electromagnetic pulse /
- photoelectron /
- secondary electron
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图 2 不同X射线注量下24 ns时圆柱体外SGEMP的电子实空间分布
Figure 2. Distribution of electrons in different fluence of X-ray at 24 ns
图 3 注量为0.4 J/cm2时的发射电流和导体吸收电流波形
Figure 3. Waveform of emitting current and absorbing current by cylinder in fluence of 0.4 J/cm2
图 4 不同X射线注量下24 ns时发射面中线(y=0，x=10.2 cm)上的的电场分布
Figure 4. Distribution of electric field on central line of emitting surface (y=0，x=10.2 cm) in different fluence of X-ray (t=24 ns)
图 5 不同X射线注量下24 ns时发射面边线(x=0, y=10.2 cm)上的磁场分布
Figure 5. Distribution of magnetic field on boundary line of emitting surface (x=0, y=10.2 cm) in different fluence of X-ray (t=24 ns)
图 7 X射线注量为4×10−2 J/cm2 ，对应两种等离子体密度(1×108cm−3 、5×109 cm−3) 24 ns时，发射面中线(y=0，x=10.2 cm)上的电场分布和发射面边线(x=0，y=10.2 cm)上的磁场分布
Figure 7. Distribution of electric field on central line of emitting surface (y=0, x=10.2 cm) and magnetic field on boundary line of emitting surface (x=0, y=10.2 cm) with fluence of 4×10−2 J/cm2 respectively in different density plasma (1×108 cm−3, 5×109 cm−3) at 24 ns
图 8 真空、低密度(1×108 cm−3)及高密度(5×109 cm−3)等离子体条件下的电磁场峰值随注量的变化
Figure 8. Peak electromagnetic field versus X-ray fluence respectively in vacuum, background plasma of low density (1×108 cm−3) or dense density (1×108 cm−3)
图 9 注量为0.4 J/cm2，等离子体密度为5×109 cm−3 时的发射电流和导体吸收电流波形
Figure 9. Waveform of emitting current and absorbing current by cylinder in plasma density of 5×109 cm−3 with fluence of 0.4 J/cm2
图 11 X射线注量为4×10−2 J/cm2时由表面光电流和次级电子共同激发的SGEMP 在50 ns时发射面中线（y=0，x=10.2 cm）上的的电场分布和发射面边线（x=0，y=10.2 cm）上的磁场分布
Figure 11. Distribution of electric field on central line of emitting surface (y=0, x=10.2 cm) and magnetic field on boundary line of emitting surface (x=0, y=10.2 cm) with fluence of 4×10−2 J/cm2 excitated by both photocurrent emitting from surface and secondary electrons at 50 ns
图 12 空气光电流能谱和角分布
Figure 12. Energy spectra and angular distribution of photoelectrons produced in air
图 13 X射线注量为4×10−2 J/cm2时由表面光电流、次级电子和空气光电流共同激发的SGEMP在50 ns时发射面中线（y=0，x=10.2 cm）上的的电场分布和发射面边线（x=0，y=10.2 cm）上的磁场分布
Figure 13. Distribution of electric field on central line of emitting surface (y=0, x=10.2 cm) and magnetic field on boundary line of emitting surface (x=0, y=10.2 cm) with fluence of 4×10−2 J/cm2 excitated by photocurrent emitting from both surface and air、secondary electrons together at 50 ns
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