A helical optical klystron for an UV-FEL project at the UVSOR

An optical klystron with helical undulators for an UV free electron laser has been designed for the UVSOR storage ring. The helical optical klystron is favorable not only to obtain higher gain but also to avoid mirror degradation because of more fundamental and less higher harmonic radiation on the axis. Characteristics of the radiation and the FEL gain for the helical optical klystron has been investigated by a calculation based on Fourier transform of Lienard-Wiechert potentials. We discuss advantages of the helical optical klystron for FELs experiments by comparing with the present UVSOR FEL by a “conventional” optical klystron.