Circular polarization with rotatable magnetic fields in crossed staggered undulator

Abstract This work presents a novel crossed staggered undulator (CSU) capable of producing circular polarization photon with higher photon energies and higher brightness. The CSU includes two 1-m long staggered undulators with 20-mm periodic length, to achieve high vertical field strength of 0.9 T and longitudinal field strength of 0.7 T at a 5.5-mm gap width. During beam injection, the staggered magnetic arrays in vacuum can be rotated within ±45° to accommodate the horizontal aperture limitation. The identical crossed magnetic fields can also be orientated to create the ideally circular or linear polarized light in any direction. The optimal merit flux is pointed at higher harmonics that allow circular polarized light to be used over the 1.4–4 KeV range in the SRRC 1.5 GeV storage ring. This paper also proposes an outline for the design of an entire system.