反向导引磁场自由电子激光中平衡态电子相轨道

PHASE ORBITS OF THE EQUILIBRIUM ELECTRONS IN A FREE-ELECTRON LASER WITH A RE- VERSED GUIDE FIELD

考虑电子束自身场情况下，给出了反向导引磁场自由电子激光中平衡态电子运动的一种正则描述。证明了在可积极限下，不动点附近相轨道的稳定性；并采用美国麻省理工学院的反向导引场自由电子激光实验参数，计算了不同束流强度下的Ｐｏｉｎｃａｒｅ截面。结果表明，即使自身场相当强（束流强度达到６０００Ａ），平衡态电子的相轨道仍保持其规则性，相空间没有出现混沌，这说明在自由电子激光器中，利用反向导引磁场可以获得比传统的采用正向导引磁场更好的电子束质量，从而改善器件的输出性能。

A canonical formulation is given of the motion of the epuilibrium electrons in a reversed-guide-field free-electron laser.It is found that the helical orbits of ele-ctrons are always stable. By generating Poincare surface-of-section maps,the influen-ces of the self-fields on the phase orbits of electrons are investigated.The resultsshow that although the current of the electron beam is Ligh up to 6000A,the phaseorbits do not become chaotic for MIT’s experimental parameters.Compared withthe case of a conventional positive-guidefield,our results indicate that using a re-versed guide field can apparently prevent the quality of the electron beam fromdegeneracy.