中文摘要：

而且，原版播种了波纹印码机线，在软 X 光检查免费电子的激光(SXFEL ) 在上海的用户设备，第二根波纹印码机线基于自我放大的自发的排放被建议与极其高的亮度完成 2-nm 激光脉搏。在这份报纸，波纹印码机 wakefields 导致的横梁精力偏差数字地被计算，并且 3D 和 2D 结果与对方一起同意很好。沿着波纹印码机的横梁精力损失降级期望的 FEL 产量表演，即，脉搏精力，放射力量和光谱，它能被补偿与一合适在波纹印码机逐渐变细。用计划解决时间诊断，一个新奇实验被建议测量 SXFEL 纵的 wakefields。

英文摘要：

Besides the original seeded undulator line,in the soft X-ray free-electron laser（SXFEL） user facility in Shanghai,a second undulator line based on self-amplified spontaneous emission is proposed to achieve 2-nm laser pulse with extremely high brightness.In this paper,the beam energy deviation induced by the undulator wakefields is numerically calculated,and 3D and 2D results agree well with each other.The beam energy loss along the undulator degrades the expected FEL output performances,i.e.,the pulse energy,radiation power and spectrum,which can be compensated with a proper taper in the undulator.Using the planned time-resolved diagnostic,a novel experiment is proposed to measure the SXFEL longitudinal wakefields.