软X射线聚束透镜特性研究

【作者】 秦义；

【导师】 李正宏；

【作者基本信息】 中国工程物理研究院 ， 核能科学与工程， 2006， 硕士

【摘要】 X射线在光导纤维中的传输特性是设计X射线透镜的基础。为设计聚焦效率高的软X射线聚束透镜，使之与软X射线源配合最大限度地获得高功率密度的软X射线束，首先对软X射线在毛细管中的传输特性进行了理论和实验研究，根据研究结果对软X射线聚束透镜参数进行设计，并制作软X射线聚束透镜，以激光等离子体作为软X射线源，对软X射线聚束透镜聚束特性进行了实验测定。 在理论模拟方面，根据光线追迹原理，建立了软X射线在弯曲毛细管中传输的计算模型，对软X射线在毛细管中传输的效率和光强分布进行了数值模拟。计算结果表明：软X射线在弯曲毛细管中的传输效率整体趋势随光子能量的增加而减小，在水窗波段较平坦，在氧K吸收边下降很陡峭；传输效率随毛细管内径的减小而增大；传输效率随毛细管曲率半径的减小而减小。 在北京同步辐射装置软X光站3W1B束线上，对不同能量软X射线(50～1500eV)在不同规格毛细管光导纤维中的传输特性进行了研究。研究结果表明：玻璃毛细管对软X射线有较高的传输效率，通过长275mm的直毛细管后，传输效率均高达80％；弯曲毛细管传输效率随软X射线光子能量的增大而减小；对相同壁厚的毛细管，随内径的增大，传输效率先增大，达到最大值后再减小；传输效率随曲率的增大而减小；对相同几何形状的玻璃毛细管，含硼(B)量越高的毛细管传输效率越高。实验结果与理论模拟结果符合较好。在我们研究的9种规格的毛细管中，使用含硼(B)量较高的DM308型号玻璃材料拉制成内径0.45mm、外径0.6mm的毛细管是组成软X光聚束透镜的最佳选择，该规格毛细管可以将能量为250eV的X射线传播方向改变26°，而出射能量达到入射到毛细管内能量的12％。 根据软X射线在毛细导管中传输的研究结果，对软X射线聚束透镜的参数进行了优化，设计并制作软X射线聚束透镜，该透镜中心长度为400mm，焦距为50mm，由1387根毛细管组成，分21层排列，毛细管由三块支架固定，收光角达到28.9°。将软X射线聚束透镜与激光等离子体软X射线源(激光脉冲半宽8ns，能量1J，基频波长1064nm)组合，在透镜后焦点处获得的软X射线束斑直径约2mm，在X射线辐射功率达到峰值时，软X射线聚束透镜总收集效率为0.8‰，整体传输效率为4.7％，，功率密度达到1.3×10~5W／cm~2，功率密度增益为825，等效距离17.8mm；在X射线脉冲辐射过程中，软X射线聚束透镜总收集效率为1.3‰，整体传输效率7.4％，功率密度增益1297，等效距离14.2mm。更多还原

【Abstract】 The basic purpose of the X-ray lens is to obtain maximum density of the X-ray radiation at the focus of the system. The X-ray transmission property of capillary is the basis for designing X-ray lens. In order to design the X-ray lens to obtain a sufficiently high concentration of X-ray radiation, the transmission character of X-ray through bending capillary is theoretically studied, experiments are carried out to measure the transmission coefficient and the parameters of the X-ray lens are optimized. As a result, the X-ray lens was made in our laboratory and experiments are carried out to study the focusing property of the new lens with the help of laser plasma as the source of soft X-ray radiation.Based on the theory of X-ray transmission through capillary, a ray-tracing method is suggested in this paper. A corresponding computer program is worked out to calculate the transmission efficiency and intensity distribution through a curve capillary. It is shown that the transmission efficiency reduces as capillary diameter increases, and increases as capillary curvature increases. The transmission efficiency generally reduces as the photo energy increases, which curve goes evenly in the "water window’ and drops sharply to K-absorption line of oxygen.The experimental results of measuring transmission efficiency within the energy range from 50eV to 1.5keV for a variety type of capillaries are presented, including different materials, different inner radius, different bent radius. It is shown that the transmission efficiency of curved capillary decreases as the X-ray energy increases, increases with the inner diameter of capillary, decreases as the bend radius of curved capillary increases. As a result, capillary manufactured of glass DM308 with inner diameter 0.45mm and outer diameter 0.60mm is the best choice for soft X-ray lens.The X-ray lens made at our laboratory consists of 1387 glass capillaries with an outer diameter of 0.6 mm, and a channel diameter of 0.45mm. The radiation capture angle is 28.9°. The focal distance is 50mm. The total lens length is 400mm. The capillaries are made of glass DM308.The focal spot diameter is about 2mm, where the maximum density of X-ray radiation 1.3 × 10~5W/cm~2 can be obtained by laser plasma. 0.8‰ of the maximum power of the source can be obtained at the output of the system, thus the transmission coefficient of the system is 4.7% and the density at the focal spot during focusing increases by a factor of 825. That result shows that at a distance of 500mm from the isotropic source the lens under consideration will give the same radiation density as that of an isotropic source without lens produces at the distance of 17.8mm. As to the total energy of the X-ray radiation, the focusing characters are as follow: 1.3‰ of the total energy of the radiation can be obtained at the output of system, the transmission coefficient is 7.4%, the density at the focal spot during focusing increases by a factor of 1297 and the same distance where the same density can be obtained without lens is about 14.2mm.更多还原