北京自由电子激光主束流输运线的研制

DESIGN OF THE ELECTRON BEAM TRANSPORT LINE FOR BEIJING FREE ELECTRON LASER

给出北京自由电子激光器主束流输运线的设计和研制结果，特别就磁铁各项技术公差对电子束品质的影响进行了计算。

AbstractThe design of electron beam transport line in Beijing Free Electron Laser is described as Fig.1. Photon-electron interaction can be induced while electron beam passing through theundulator.Electrons travelling in planar periodic magnet field,would oscillator with the same period ofthe undulator and an amplitude much small compared to bunch radius.The longitudinal fieldcomponent causes a focusing Betatrom oscillation. Like Fig.2,single electron trajectory wascomputed with the code TRWIG developed by us. The 90°achromatic bend consists of two 45°dipole magnets and two quadrupoles.Whilethe latter focus beam in houizontal plane,the former is designed with edge focusing on verticalplane which helps to form a achromatic waist in the undulator by tuning.the bend is nearly isochronous,when the energy spread of the electron bema is not large justas BF conditions.For proper lasing,the electron beam should overlap with the optical beam,and the positionof the waist of the beam envelop should be easily adjusted along the undulator axis.Fig.3 isthe beam envelop from the exit of linac to the end of undulator.the 180°bend system is symmetrical and consists of four 45°dipole magnets the same asthose used in 90°bend,and five quadrupole magnets which can be manipulated so that the beamcan pass through a distance and be matched into the energy spectrometer.