MODE COMPETITION AND CONTROL IN FREE-ELECTRON LASERS WITH ONE-DIMENSIONAL AND 2-DIMENSIONAL BRAGG RESONATORS

We present a time domain analysis of the transverse mode dynamics whic h occur in FEL oscillators using oversize microwave cavities. It is sh own that both traditional one-dimensional and novel two-dimensional Br agg cavities can produce radiation at a single frequency with a one-mo de azimuthal distribution, which corresponds to spatial synchronizatio n of the electromagnetic radiation. In one-dimensional system, electro nic mode selection occurs via nonlinear mode competition. In contrast, electrodynamic mode selection occurs in two-dimensional Bragg cavitie s, resulting in the production of a single azimuthally-symmetric mode after the linear stage of evolution. The two-dimensional Bragg cavity is shown to retain its selectivity when its radius greatly exceeds the radiation wavelength.