进化多目标优化算法产生大带宽X射线自由电子激光
Generation of large-bandwidth x-ray free electron laser with Evolutionary Many-Objective Optimization Algorithm
摘要：
X射线自由电子激光（XFEL）是广泛应用于各个学科的尖端科学仪器。传统上，在XFEL中追求窄带宽。近年来，大带宽XFEL被广泛应用于X射线光谱学和X射线晶体学研究，其中过压缩技术是一种通过提高电子束能量啁啾来产生宽带宽XFEL脉冲的有效方法。本文结合克服相干同步辐射引起的横向切片失准的束流偏转校正，将寻找直线加速器过压缩工作点问题处理为多目标优化问题，首次将非支配排序遗传算法Ⅲ应用于束流动态优化。对上海软X射线自由电子激光用户装置的全带宽进行了模拟计算，结果表明全带宽为4.6%。
英文摘要：
X-ray free-electron lasers (XFELs) are cutting-edge scientific instruments for a wide range of disciplines. Conventionally, the narrow bandwidth is pursued in an XFEL. However, in recent years, the large-bandwidth XFEL operation schemes are proposed for X-ray spectroscopy and X-ray crystallography, in which over-compression is a promising scheme to produce broad-bandwidth XFEL pulses through increasing the electron beam energy chirp. In this paper, combining with the beam yaw correction to overcome the transverse slice misalignment caused by the coherent synchrotron radiation, finding out the over-compression working point of the linac is treated as a many-objective (having four or more objectives) optimization problem, thus the non-dominated sorting genetic algorithm III is applied to the beam dynamic optimization for the first time. Start-to-end simulations demonstrate a full bandwidth of 4.6% for Shanghai soft x-ray free-electron laser user facility.
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