Segmented Undulator for Extensive Polarization Controls in ≤1 nm-rad Emittance Rings

We designed a segmented undulator composed of four units of an APPLE undulator, such as an APPLE-II, and three phase-shifters. By simulating the optical performance in a 1-nm-rad emittance ring of synchrotron radiation, the novel undulator generates various polarized light that have high flux, high polarization, and fast-switching with a marginal perturbation to an electron beam in the storage ring. Varieties of polarization combinations in undulator segments allow for novel research, such as experiments using orbital angular momentum in X-ray photons. Furthermore, they provide a high flux third harmonic beam for both linear and circular polarizations, extending the photon energy range significantly at a beamline. The high degree of freedom in polarization controls of the segmented undulator provides opportunities for new experiments with low-emittance synchrotron radiation or X-ray free electron lasers.