Z-w. Dong*, K. Masuda, T. Kii, T. Yamazaki and K. Yoshikawa
Institute of Advanced Energy, Kyoto University
A space-time dependent, multi-frequency FEL oscillator simulation code has been developed by using the transverse mode spectral method to analyze the laser mode dynamics. In this code the electron beam is modelled by a group of super particles which have density profiles in both the transverse and longitudinal directions. The energy spread and the finite emittance of the electron beam are also included, while the optical field is expressed in terms of an expansion of normal resonator modes. Hence this code enables us to study the longitudinal profile and transverse structure of FEL at the same time.
In this paper, evolution of the longitudinal mode structure of a short pulse FEL oscillator is calculated in order to investigate the effects of cavity detuning, power output coupling factors, and transverse mode competition on radiation
build-up.
