Polarization switching of segmentally helical undulators in a diffraction-limited storage ring

Abstract

Polarization switching of synchrotron radiation has wide application prospects in various areas, requiring a high switching frequency between horizontally linear polarization (HLP) and vertically linear polarization (VLP) or between left-hand circular polarization (LCP) and right-hand circular polarization (RCP). To make it possible for realizing a fast polarization switching, in this paper we simplify and incorporate the previous schemes based on segmentally helical undulators connected by phase shifters. Adjacent undulators are set by the same or opposite polarization state to generate circularly or linearly polarized radiation. Theoretical analysis and simulations for radiation characteristics are reported in details. By combining the polarization adjustment of each helical undulator with the phase shifters, both the switching for HLP/VLP and LCP/RCP can be realized in the same undulator scheme. The on-axis heat load can always be effectively suppressed. Benefiting from the extremely low emittance and taking into account the space occupied by phase shifters, the proposed scheme shows a significant advantage in preserving the photon flux with a high polarization degree in a diffraction limited storage ring compared with a typical third generation storage ring. In addition, we also study the influence of beam deviation at each undulator segment, the segment number limited by the practical length of straight section and the issues related to user experiments.