Helical wigglers for the OK-5 storage ring VUV FEL at Duke

In this paper, we present the design and parameters of electromagnetic wigglers with controllable polarization for the VUV OK-5/Duke storage ring FEL. The OK-5 FEL, the first distributed optical klystron, is comprised of four wigglers and three matching sections with individually controlled quadrupoles and bunchers. The geometry and the relative strength of horizontal and vertical fields determine the polarization of the radiation from the OK-5 wigglers. We compare the predicted and measured quality of the wiggler fields.