FEL OSCILLATION ON TERAS

In the laser oscillation experiment on the storage ring TERAS, the imp rovement of the beam quality is quite important due to the extremely l ow gain of the TERAS FEL system. A second harmonic rf cavity (Landau c avity) is installed in TERAS to suppress the beam instability which de grades the beam quality. By observing the beam parameters, such as ene rgy spread and transverse beam sizes systematically, it was proved tha t the Landau cavity is effective to improve the beam quality at a beam current less than approximately 7 mA/bunch. A Q-switching experiment was carried out by changing the frequency (171.62 MHz) of the rf, fed to the main rf cavity, by 500 Hz with a modulation frequency of 2.2 Hz . The oscillation behavior was changed from a random-pulse manner, to a periodic oscillation and the peak power was increased by a factor of approximately 5 with the Q-switching operation.