• K. Hayakawa, Y. Hayakawa, K. Nakao, K. Nogami, T. Sakai, I. Sato, T. Tanaka
  LEBRA, Funabashi

Funding: "Academic Frontier" Project for Private Universities: matching fund subsidy from MEXT (Ministry of Educatin, Culture, Sports, Science and Technology), 2000-2004

In general, maximum gain and maximum power of a free-electron laser (FEL) oscillator are not simultaneously satisfied at an identical length of the optical resonator. Use of a short bunch electron beam, therefore, can cause a large fluctuation of gain and saturated power of the FEL due to only a small change in the resonator length. If the length of the resonator can be adjusted at the middle in the macropulse duration of the electron beam, both maximizing conditions will be satisfied simultaneously, which will result in a large FEL output power compared with a normal operation. Since it is difficult to change the length of the resonator during the macro pulse, modulation of the bunch interval has been attempted for the LEBRA FEL system by modulating the phase of the accelerating rf of the electron linac, which has an equivalent effect to change of the resonator length. The modulation of the rf phase has resulted in intensification of the output energy per macro pulse by approximately twice compared with that in normal operation, which is consistent with numerical simulation.