A design study on electron beam confinement in a staggered array undulator based on a 3D code

A staggered array undulator is implemented to improve the electron beam confinement. A staggered array undulator has an inherent vertical focusing force, but it has no horizontal focusing force, resulting in a beam loss. To improve the electron beam confinement with an additional horizontal focusing force, the geometrical shape of the ferromagnet pieces were refined by use of a newly developed 3D code. As a result, the number of electrons, which can pass through the undulator, was found to increase by 10%, and consequently, the spontaneous emission intensity also increased by 10%. Transmittance of a 4 MeV electron beam is found to be 99.7% for an undulator of 0.5 m length and 5 mm gap width. Also, for a longer undulator of 2.0 m length, the transmittance is found still high up to 97.3%.