DESIGN OF A 6.3-M OPTICAL KLYSTRON FOR A STORAGE-RING ULTRAVIOLET FREE-ELECTRON LASER

A 6.3-m optical klystron (OK) to be used for free-electron laser (FEE) experiments with wavelength from visible to ultra-violet is now in the stage of design. The OK will be installed in a 7.25-m straight section of a racetrack-type storage ring NIJI-IV dedicated to FEL. Pure permanent-magnet blocks made of NEOMAX-35H are used for the OK. The number of periods (72 mm) in each normal-undulator section is 42 with 18-mm thickness, and the dispersive section is 216 mm long and 36 mm thick. Each of the sections will be constructed separately, but the actuators will be driven either in synchronism or independently. With the above configuration, the FEL oscillation with wavelength ranging from 600 to 200 nm is expected by changing the electron-beam energy from 200 to 400 MeV. The FEL gain is estimated, to be about 4.8 x 10(-3)/mA per bunch at 600 nm, and 2.2 x 10(-3)/mA per bunch at 350 nm. Here, the degradation due to the filling factor is neglected and the relative energy spread is conservatively assumed to be 7.5 x 10(-4). The effect of the long OK on the electron beam is also estimated.