Jump-over method of the FEL interaction among electron beam bunches for increasing the radiation power

A new method to substantially increase the FEL radiation power in an electron storage ring is presented. In this method, the storage ring is operated with many bunches, and the FEL interaction of a light pulse with the beam bunches is jumped over for several bunches by modulating the closed orbit distortion of the stored beam in synchronism with the FEL interaction. The interaction interval for each bunch is lengthened considerably, and the radiation damping proceeds for a longer time. The energy spread is much reduced and the radiation power can be increased more than a factor of 10.