上海软X射线自由电子激光装置(SXFEL)是中国第一台X射线相干光源,其辐射波长可覆盖水窗波段。为满足不同的用户需求,装置将加装椭圆极化波荡器,运行模式可在线偏振与圆偏振之间切换。基于SXFEL装置对偏振控制方案进行参数设计,评估了电子束抖动的影响,并在理论上分析了该方案的辐射稳定性。此外,还设计了一套圆偏振方向的快速切换结构,它可使SXFEL装置以10 Hz频率量级在不同的圆偏振方向之间切换。

The Shanghai Soft X-ray Free-Electron Laser (SXFEL) Facility is the first coherent X-ray light source in China with a wavelength covering the water window. An elliptically polarized undulator (EPU) will be installed to meet the needs of different users, so that the output laser can be switched between linear polarization and circular polarization. This paper presents the polarization control design for the user facility, the evaluation of bunch energy jitter, and analysis of radiation power stability. Moreover, a switching structure of the circular polarization direction is also designed, so the polarization of the output laser can be switched between opposite directions on the base of permanent magnet oscillator at the rate of tens of Hz.