The VUV/UV OK-5 Duke storage ring FEL with variable polarization

We discuss the design and expected performance of the OK-5 FEL, which will replace in 2002 the OK-4 FEL operating now at the Duke storage ring. The OK-5 FEL is the first distributed optical klystron with variable polarization. The design of wigglers and matching sections is flexible for providing optimal conditions for variety of operation modes. In this paper we present calculations of the main OK-5 FEL parameters such as its tuning range, gain and lasing power. Based on our calculations we present the predictions for the OK-5 gamma-ray source. We conclude with description of the current status of the OK-5 FEL and plans for its installation.