波荡器电子轨迹中心偏移和磁场误差对CTFEL装置性能影响很大, 通过前期设计和后期测量与优化将其限制在指标要求范围内。在前期设计中尽量避免引入全局性的系统误差: 磁结构具有平面反对称结构, 保证电子轨迹中心和波荡器磁轴重合; 磁结构端部的特殊设计减弱了间隙对出口磁场二次积分的影响; 机械系统的大梁和立柱具有良好的刚性, 闭环控制系统保证了高的波荡器间隙控制精度, 这些措施降低了间隙不一致引入的磁场误差。在后期测量与优化中削弱了磁场的残存全局系统误差和局部随机误差: 利用磁场点测台测量了波荡器磁场的纵向和横向分布, 通过调节标准单元组件位置对磁场进行了垫补和优化, 优化后电子轨迹中心偏移、峰峰值误差、相位误差、好场区及其误差均满足指标要求。

Electron trajectory center deviation and magnetic field errors of undulator have a great influence on the performances of CTFEL facility, which were limited in the range of specification requirements by preliminary design and post measurement and optimization. In the preliminary design, the global system errors were avoided as far as possible: the magnetic structure has a planar anti-symmetric structure to ensure the coincidence of electron trajectory center and undulator magnetic axis; the special design of magnetic structure end weakens the influence of gap on second integral of magnetic field at undulator exit; the beam and frame of the mechanical system have good rigidity and the control system with close-loop configure guarantees high accuracy of the gap control, all of which limit the magnetic field errors caused by the gap inconsistency. The residual global system errors and local random errors of the magnetic field were reduced in the later measurement and optimization: the longitudinal and transverse distributions of magnetic field were measured using magnetic field measurement bench and then the undulator field was shimmed and optimized by adjusting the positions of standard unit components. Finally, the electron trajectory center deviation, peak-to-peak error, phase error and good field range error meet the requirements of specification after optimization.