坡度摇摆器自由电子激光中电子运动的稳定性分析

Stability of the Electron Motion in a Free-electron Laser with Tapered Wiggler

提高自由电子激光器效率和功率的方法之一,是采用坡度摇摆器来延缓束波互作用进入饱和。本文通过计算柯尔莫哥洛夫熵(Kolmogorov entropy,简称K熵)来研究坡度摇摆器自由电子激光器中电子运动的稳定性,结果表明:无坡度时平衡态电子的柯尔莫哥洛夫熵值在零附近振荡,有坡度时K熵值趋于负值,稳定性变好;当激光从电子获得能量并呈指数增长时,引起K熵值涨落,不宜采用正坡度而应采用负坡度方能改善电子运动的稳定性。

One of the methods in enhancing the efficiency and output of a free-electron laser is the use of a tapered wiggler for post-ponement of the beam-wave interaction saturation .In this paper, the electron motion stability in a free-electron laser with tapered wig-gler is studied by means of the Kolmogorov entropy （ K-entropy ） .It is shown that values of K-entropy of the equilibrium electron oscil-late around zero when the wiggler is un-tapered, whereas values of K-entropy end to the negative value when the wiggler is tapered and consequently the motion stability is improved .It is found that the laser fields exponentially growing by extracting the kinetic energy of the electron beam cause heavy fluctuation of the K-entropy , and instead of a positive taper , a negative taper should be employed so as to improve the stability of the electron motion .