Generation and spatial separation of circular polarized FEL radiations by orbit control

Circularly polarized radiation in the X-ray region is required by many experimental applications. Such demands can be met at FEL facilities by mounting few helical undulators after the planar undulators. For obtaining high degree of circular polarized radiation, the reverse taper technique is often used, where in the planar section, significant bunching of the electron beam is accumulated while the output linear polarized radiation power is suppressed. This paper investigates the technique of spatially separating the background weak linear radiation by first transversely deflecting the electron beam with dipole kicker magnets in the planar undulator section and correcting its orbit and traveling direction before entering the helical undulators. The resulting linearly and circularly polarized radiations will propagate in slightly different directions and can be separated spatially. Numerical simulations are performed to analyze the impact of electron beam deflection on the radiation properties.