Simulation study of ultrashort intense laser experiment associated with electromagnetic pulse
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摘要: 靶室腔体谐振产生的电磁辐射是超短超强激光与靶相互作用实验中生成的电磁脉冲(EMP)来源之一。基于有限元分析方法，对靶室腔谐振产生电磁脉冲和电磁脉冲通过窗口向外传播这两个过程进行仿真模拟。前者模拟获得空腔和含结构模型谐振时特征磁场，结果显示内部结构对电磁场强度分布和谐振频率有显著影响；后者模拟结果显示，窗口外侧电场强度比窗口内侧高约40%，而且电磁脉冲传播到靶室外后呈球面波形式扩散并衰减。对电磁脉冲的强度衰减规律进行了分析，得到该衰减曲线的拟合函数。Abstract: The electromagnetic radiation produced by the resonance of the target chamber is one of the sources of electromagnetic pulse generated in the experiment of ultra-short intense laser and target interaction. Based on the finite element analysis method, we simulated the two processes of the electromagnetic pulse produced by the resonance of cavity and electromagnetic pulse propagating outward through windows. The former results show that the internal structure has a significant influence on the intensity distribution and resonance frequency of the electromagnetic field. The latter simulation results show that the electric field intensity outside the window is about 40% higher than that inside the window, and the electromagnetic pulse propagates to the target outside and then spreads and attenuates in the form of spherical wave form. The intensity attenuation rule is analyzed and the fitting function of the attenuation curve is obtained.
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图 1 柱状空腔和含内部结构靶室模型(单位：m)
Figure 1. Columnar cavity (a) and the internal (b) structure target chamber model (unit: m)
图 2 (a) 模拟模型空腔时磁场分布；(b)腔室内包含棱镜、金属镜架、金属平板、玻璃窗等组件时的磁场分布；白色箭头表示磁场通量
Figure 2. (a)Magnetic field of the simulated fundamental model; (b) A distortion of the magnetic field in the target chamber filled by the metal plate, lens, metallic lens holder and window; the arrows indicate the magnetic field flux
图 3 (a) 柱形模型腔室(内包含棱镜、金属镜架、金属平板、玻璃窗等组件)在194.8 MHz频率处谐振时内部的磁场空间分布；(b)~(d)为顶部和侧面的磁场视图
Figure 3. (a)Simulation of the magnetic flux density distribution in the cylindrical target chamber for the resonant frequency of 194.8MHz by inserting the metal plate, lens, metallic lens holder and window.(b)~(d) Top and sides projections of magnetic field inside the target chamber
图 4 各时刻电磁场强度分布图; 曲线为电场强度的等值线，图(a)显示A, B, C三点的相对位置
Figure 4. Simulation of the electromagnetic field intensity distribution; the curve is the contour line, figure (a) shows the relative position of the points A, B, C
图 5 A, B和C三点处电场强度随时间变化曲线
Figure 5. The time curve of the intensity of the electromagnetic field at points A, B and C
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