低能注量X射线辐照下圆柱腔内辐射环境及IEMP的模拟研究

Simulation of Radiation Environment and IEMP Irradiatedby Low Energy Fluence X Ray in Cylindrical Cavity

通过MCNP程序模拟计算了低能注量X射线辐照圆柱腔外端面并透射进入腔体时,腔内各作用面的综合辐照环境及电子发射参数。结合3维粒子模拟(PIC)程序,对多发射面作用下圆柱腔内电磁场和粒子分布进行了模拟计算,并与仅存在上端面电子发射时的电磁场结果进行对比。结果表明,在实际情况下,圆柱侧壁和下端面会发射大量电子,能将上端面中心处的轴向电场强度增大至仅上端面发射电子时的2倍,而由于此时腔内多发射面作用下电流方向的复杂化,磁场强度则略微减小。同时,比较了由MCNP计算得到的前向散射电子能谱和部分文献采用的近似能谱,分别提供电子发射速度时内电磁脉冲(IEMP)的电场强度波形。结果表明,能谱的改变会对电磁场带来极大的改变,故建议通过相关蒙特卡罗(MC)程序计算IEMP电子发射能谱。

MCNP was adopted to give the irradiation environment and the electron emission parameter of each internal emission surface under the low energy fluence X ray illuminating perpendicularly to the external head surface of the cylinder and penetrating inside.And the 3D particle-in-cell(PIC)code was combined to calculate the electromagnetic field and particle distribution when different surfaces emit electrons at the same time,and the results were compared with those when only the internal head surface was set as the emission surface.The result indicates that on the account of the plenty of electrons emitted from the side wall and end surface in the cavity,the electric field intensity on the head surface is enlarged significantly over 2 times,while because the electrons are emitted from different emission surfaces,the total current is relatively complex,resulting in the decrease of the magnetic field intensity.Meanwhile,two groups of normal electric field intensity under different energy distributions from MCNP and approximate value by early references separately were compared.The result shows that energy distribution will greatly change the electromagnetic field,and it is still necessary to calculate energy distribution of IEMP by Monte Carlo codes.