Yang Xi, Li Junjie, Fedurin Mikhail, Smaluk Victor, Yu Lihua, Wu Lijun, Wan Weishi, Zhu Yimei, Shaftan Timur
Brookhaven National Laboratory, Upton, NY, 11973, USA.
ShanghaiTech University, Shanghai, China.
Sci Rep. 2019 Nov 20;9(1):17223. doi: 10.1038/s41598-019-53824-9.
A real-time, nondestructive, Bragg-diffracted electron beam energy, energy-spread and spatial-pointing jitter monitor is experimentally verified by encoding the electron beam energy and spatial-pointing jitter information into the mega-electron-volt ultrafast electron diffraction pattern. The shot-to-shot fluctuation of the diffraction pattern is then decomposed to two basic modes, i.e., the distance between the Bragg peaks as well as its variation (radial mode) and the overall lateral shift of the whole pattern (drift mode). Since these two modes are completely decoupled, the Bragg-diffraction method can simultaneously measure the shot-to-shot energy fluctuation from the radial mode with 2·10 precision and spatial-pointing jitter from the drift mode having wide measurement span covering energy jitter range from 10 to 10. The key advantage of this method is that it allows us to extract the electron beam energy spread concurrently with the ongoing experiment and enables online optimization of the electron beam especially for future high charge single-shot ultrafast electron diffraction (UED) and ultrafast electron microscopy (UEM) experiments. Furthermore, real-time energy measurement enables the filtering process to remove off-energy shots, improving the resolution of time-resolved UED. As a result, this method can be applied to the entire UED user community, beyond the traditional electron beam diagnostics of accelerators used by accelerator physicists.
通过将电子束能量和空间指向抖动信息编码到兆电子伏特超快电子衍射图案中，对一种实时、无损的布拉格衍射电子束能量、能量展宽和空间指向抖动监测器进行了实验验证。然后将衍射图案的逐次波动分解为两种基本模式，即布拉格峰之间的距离及其变化（径向模式）和整个图案的整体横向偏移（漂移模式）。由于这两种模式完全解耦，布拉格衍射方法可以同时测量径向模式下精度为2·10的逐次能量波动以及漂移模式下具有宽测量范围的空间指向抖动，该测量范围覆盖从10到10的能量抖动范围。这种方法的关键优势在于，它使我们能够在进行中的实验过程中同时提取电子束能量展宽，并能够对电子束进行在线优化，特别是对于未来的高电荷单次超快电子衍射（UED）和超快电子显微镜（UEM）实验。此外，实时能量测量使滤波过程能够去除能量异常的脉冲，提高时间分辨UED的分辨率。因此，这种方法可以应用于整个UED用户群体，而不仅仅局限于加速器物理学家所使用的传统加速器电子束诊断。
