短波长自由电子激光器电子运动特性研究

短波长自由电子激光器的电子束在摇摆器中的传输通道长而狭窄, 须得电子具有良好的运动特性, 避免在传输过程中产生横向发散. 本文研究短波长自由电子激光器中超相对论电子在磁场具有横向分布的平面摇摆器中的三维运动特性, 用逐次逼近法推导相对论运动方程的解析表达式, 非线性数值计算模拟传输过程, 采用科尔莫 戈罗夫熵 方法分析运动的稳定性. 结果表明: 摇摆器磁场除使电子做周期性摇摆运动外, 还迭加了偏离轴线的横向漂移运动, 在没有外置的磁场聚焦系统情况下, 电子将偏离轴线横向发散; 但是, 恰当选取电子的横向初始速度, 可有效地防止电子运动的横向发散, 即使没有外置的磁场聚焦系统, 也能在长达10 m 的摇摆器中顺利传输, 横向位移范围不超过0.09 mm, 而且其运动是稳定的. 关键词： 短波长自由电子激光器 平面摇摆器 超相对论电子运动 运动稳定性

Characteristics of electron motion in a short-wavelength free-electron laser

Transport channel of the electron beam in a short-wavelength free-electron laser is quite narrow and long, which is needed for the electrons to have excellent motion feature so as to prevent the transverse divergence. In this paper the characteristics of the ultra-relativistic electron motion in a planar wiggler filed with transverse distribution are studied by analytical derivation, nonlinear simulations and Kolmogorov entropy calculations. Results show that the wiggler not only forces the electron to periodically wiggle on the transverse plane, but also superpose a transverse shift motion leaving away from the wiggler axis, which leads to the transverse divergence of the electron motion in the absence of an external magnetic focusing system. However, it is shown that the proper choice of the initial value of the electron transverse velocity could suppress the transverse motion divergence, where the electron can smoothly pass through a narrow and long channel with a length of 10 m and a width of 0.09 mm and the electron motion is stable even if there is no external magnetic focusing system.
Keywords： short-wavelength free-electron laser planar wiggler ultra-relativistic electron motion motion stability