Z箍缩X射线源辐射场理论分析

Analysis of Radiation Field for Z-pinch X-ray Source

利用Z箍缩等离子体辐射源产生X射线可开展脉冲X射线辐照材料动力学响应及热力学效应研究,而试验面处的辐射功率密度是热力学效应研究中最关心的参数。本文针对Z箍缩产生的软X射线辐射功率密度场分布,以理论分析和数值模拟为手段,将Z箍缩软X射线辐射源分别等效为线光源和朗伯辐射光源,获得了2种等效情况下X射线辐射功率密度场的分布。分析表明,在线光源等效情况下,远场分布为球面分布,符合距离平方反比关系,而近场则近似圆柱面分布,符合距离反比关系;在朗伯辐射光源等效情况下,远场分布为球面余弦调制分布,而近场分布近似圆柱面分布。等效模型分析结果均表明:对于长度为2 cm的Z箍缩软X射线辐射体,当试验样品放置位置距离Z箍缩光源大于5 cm后,试验面处的辐射功率密度即可视为远场情况,符合距离平方反比关系。

The Z-pinch is the most powerful X-ray source which can be obtained in the laboratory and it can be applied for many research fields,such as high energy density physics,inertial controlled fusion and laboratory astrophysics.In material experiments the Z-pinch X-ray source is utilized to radiate the material for carrying out thermodynamic effect researches,which are important for the radiation-hardened reinforcement design of the system.In these experiments the radiated X-ray power density acted on the sample is one of the most important parameters concerned by the researchers.In this paper the radiation filed of a Z-pinch soft X-ray source was analyzed.The Z-pinch X-ray source was treated as a line source and a Lambert radiation source or called as cosine radiator respectively.Based on the fundamental optical rules the expression was deduced which illustrated the X-ray power density radiated by the Z-pinch source.For the line source model,it shows that the radiation power density in the far filed is inversely proportional to the square of the distance from the source,and the contour surface is the conventional sphere surface,while in the near filed the radiated power density is inversely proportional to the distance,and the contour surface is more like a cylindrical surface.For the cosine radiator model the radiated power density in the far filed is still proportional to the square of the distance from the source,and the contour surface is a modified sphere surface which is multiplied by the cosine value of the angle.In the near filed the cosine radiation source model gives the same distribution for the radiated power density as the line source model.Based on the analysis mentioned above the radiation power density on the sample at QiangguangⅠaccelerator was investigated.In QianguangⅠexperiments the sample was located 5 cm far from the central Z-pinch source,which implies that the distance is comparable with the size of the Z-pinch source.The analysis results show that the power density radiated of the assessed material is inversely proportional to the square of the distance from the material to the source.In another word the radiation power density of the sample is satisfied the far filed criterion providing that the sample is located further than 5 cm,so it is reasonable in the experiments on QiangguangⅠthat the power density radiated of the sample can be obtained by measuring the power density at the point which is further than 5 cm.