屏蔽电缆对脉冲X射线响应的数值计算

Responses of shielding cable to pulsed X-rays

结合蒙特卡洛方法和时域有限差分(FDTD)方法,计算了电缆受脉冲X射线辐照时介质层内的运流电流密度,并以此为麦克斯韦方程的源,计算得到了电缆两端接匹配负载时的芯线响应电流。该方法综合考虑了电缆芯线、介质层和屏蔽层的沉积电荷对芯线响应电流的影响。计算结果表明:芯线响应电流大小与电缆受辐照长度成正比,电流由辐照中心向两边流走;源区越靠近中心位置,电流幅度越小,源的中心位置处,电流为零,源区存在静电场;源区外,电流大小相等,方向相反。最后,利用有限差分法计算得到的电场强度反推出了芯线电荷数,与蒙特卡洛方法计算的结果相比,FDTD方法计算的要低20%,该误差可能由将3维问题近似为1维问题所引起。

For purpose of getting the radial electric current density in the medium of the cable due to X-rays illumination, Monte Carlo method and Finite-Difference Time-Domain （FDTD） method are used. Using the radial electric current density as the source of Maxwell functions, center conductor response current is calculated under the condition of matching load of cable ends. Distributed charges in center conductor, medium and shielding are considered in this method. The results show that the center conductor response current is proportional to the length of the illumination, and it is in the opposite direction of the source. In source zone, there is static field. The distributed charge of the center conductor is calculated using electric field, and it is about 20% less than the solution of Monte Carlo method, which is aroused by approximation.