一种小尺寸轫致辐射转换靶设计

Small sized bremsstrahlung conversion target

以减小直线感应加速器X射线光源横向尺寸为目标,开展轫致辐射转换靶的设计。对聚焦打靶过程中电子束运动轨迹进行分析,指出同一个电子束轨迹分布,既可以描述为电子束在某纵向位置处具有一定的横向展宽,也可以描述为电子束保持较小横向尺寸时的轴向分布展宽,由此提出在束腰附近放置多个小靶片实现聚焦电子束有效阻挡的小尺寸多层靶概念设计。采用EGS4程序对X射线产额进行计算,发现靶厚度在一定范围内改变时X射线产额变化较小,基于这一规律完成了小尺寸多层靶的结构设计。进一步考察了一个设计应用实例,当聚焦电子束最小包络直径3 mm、会聚角100 mrad时,对比大尺寸靶,采用小尺寸多层靶可以获得等效直径减小约50%、产额减小约10%的X射线光源。该设计方法有望在相同的电子束品质和聚焦条件下,获得横向尺寸小于电子束最小束包络直径的X射线光源,具有一定的应用价值。

The paper aims to reduce the lateral size of the X-ray source in a linear induction accelerator and design a bremsstrahlung conversion target.Analyzing the trajectory of the electron beam during the focused shooting process,it is pointed out that the distribution of the same electron beam trajectory can be described as either the transverse broadening of the electron beam at a certain longitudinal position or the axial distribution broadening when the electron beam maintains a small transverse size.Therefore,the concept design of a small-sized multi-layer target with multiple small targets placed near the waist to effectively block the focused electron beam is proposed.The EGS4 program was used to calculate the X-ray yield,and it was found that the change in X-ray yield was relatively small when the target thickness changed within a certain range.Based on this rule,the structural design of a small-sized multi-layer target was completed.Further investigation was conducted on a design application example.When the minimum envelope diameter of the focused electron beam is 3 mm and the convergence angle is 100 mrad,compared to large-sized targets,using a designed small-sized multi-layer target can obtain an X-ray light source with an equivalent diameter reduction of about 50%and a yield reduction of about 10%.By adopting the proposed design method,it is expected to obtain X-ray light sources with lateral dimensions smaller than the minimum envelope size of the electron beam under the same electron beam quality and focusing conditions,which has certain application value.