First lasingand initial operation ofa circularly polarized optical klystron ok-5 felandavariably polarized distributed optical klystron DOK-1 FEL at DUKE
To improve the capability and performance of its light sources, the Duke FEL lab (DFELL) is upgrading its storage ring based FEL. The existing linearly polarized OK-4 FEL wigglers are being replaced gradually by the next generation OK-5 wigglers capable of producing either linearly or circularly polarized light. In the second phase of this upgrade in 2005, the OK-5 FEL consisting of two wigglers is installed together with the OK-4 FEL in a specially designed magnetic lattice. The circularly polarized OK-5 FEL was first brought to lasing on Aug. 14, 2005. In the following days, the first distributed optical klystron FEL with variable polarization, the DOK-1 FEL, comprised of two horizontal OK-4 wigglers and two circular OK-5 wigglers, was brought to lasing for the first time. In this paper, we report our commissioning experience and initial measurements of both the OK-5 FEL and DOK-1 FEL.