Simulation for measurement technique of electron beam divergence basing on Cherenkov radiation
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摘要: 利用切伦科夫辐射方向性极好的特性进行电子束发散角的测量是一个比较有希望的方法，但转换靶材料对电子的库伦作用力等因素又使得电子束散角展宽，对发散角的测量产生影响。在将转换靶划分成多重薄片并以串联的形式构建了靶模型，考虑了库仑力、多重散射、轫致辐射、电离等全物理过程作用效果的情况下，利用蒙特卡罗模拟软件相关程序对电子在靶材料中的发散过程进行了仿真。基于电子束散角分布与切伦科夫辐射光子分布相对应的原理，完成了对电子束发散角测量技术的模拟，获得了转换靶材料及其厚度、电子束能散、测量系统光学带宽等对电子束发散角测量的影响规律，为测量系统的设计及数据反演处理工作提供了指导性的建议。模拟结果显示，基于切伦科夫辐射进行电子束发散角测量的方法具有可行性，具有一定的对电子束发散角分布进行测量的能力。Abstract: The direction of Cherenkov Radiation (CR) light is strictly defined by the direction along which the charged particle moves. This characteristic can be adopted to measure the electron beam divergence and it is a hopeful method. The Coulomb force on electron in the convertor expand the beam divergence and obviously reduce the measurement precision. A model of multi-slice in cascade connection is adopted to constitute convertor configuration. Taking into account the combined effect of Coulomb force, multiple scattering, bremsstrahlung and ionization, the deviation process of electron in the convertor material is then simulated by Monte-Carlo simulation. Measurement technique of electron beam divergence is further simulated basing on the principle of exact corresponding relationship between electron beam divergence distribution and CR photon distibution. Some effect on measurement are obtained for factors including convertor material, thickness, beam energy divergence and optical bandwidth of measurement system. The simulated results give many useful suggestions for the design of the measurement system and the image data processing. The simulation results obviously show the feasibility of electron beam divergence measurement basing on Cherenkov radiation and that its distribution can also be measured in a certain extent.
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图 2 基于测量系统的模拟工作布局原理
Figure 2. Layout of the simulation work basing on measurement system principle
图 3 理想电子束经不同厚度SiO2后的发散图像
Figure 3. Divergence images for ideal electron beam after passing through SiO2 slice with different thickness
图 4 不同厚度下SiO2及Mylar薄膜的冲击响应函数
Figure 4. Impulsion response function of SiO2 slice and Mylar film with different thickness
图 5 转换靶折射率对散角分布测量的影响规律研究
Figure 5. Influence of index of SiO2 detector on beam divergence
图 6 不同发散角的测量精度模拟
Figure 6. Measurement precision simulation for different beam divergence
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