Research & Development of a Variable Polarisation Superconducting Undulator at the NSLS

In this paper a new concept for a planar, superconductive, variable polarization undulator (VPU) is presented. Advantage of this design include: (1) electrical tunability for both right and left circular and elliptical, as well as linear vertical or horizontal, (2) it requires no compensation of unwanted vertical field component and (3) used only simple windings of superconductive wire in an interlaced pattern. The construction of the device is described and compared with a permanent magnet VPU with the same gap and period, as well as with previously published concepts.