Lawrence Berkeley National Laboratory

A concept utilizing superconducting magnets for variable polarization insertion devices is presented. The iron-free design enables full variable linear and elliptical polarization over a broad spectral range. With appropriate electrical switching the same device can access higher energies through period-halving, while continuing to provide variable-linear polarization; furthermore, separate switching will allow for period-doubling with full linear and elliptical polarization control. The performance, both in terms of field/spectral performance and in terms of polarization control, is compared to existing permanent magnet EPU devices. Engineering issues associated with the fabrication and implementation of the device are discussed.