FEL ON SLOW CYCLOTRON WAVE

A theory of linear and nonlinear interaction of fast electromagnetic w aves with a slow cyclotron wave of relativistic electron beam in an FE L with circularly polarized wiggler field and longitudinal guide field is presented. It is shown that such interaction is a twice parametric process with regard to the wiggler field. As a result the spatial gro wth rate of the electromagnetic wave in the linear regime, and the inh erent efficiency of interaction are smaller than those for the undulat or synchronism. The optimal length of the interaction region is also f ound to be larger. Nevertheless, within the certain limits of the posi tive guide field strength the operational frequency of a slow cyclotro n wave FEL can be higher than that of the standard FEL and the resulta nt efficiency of an EEL-oscillator in the millimeter wavelength range can be of 5-10%. The use of the wiggler or guide field tapering to opt imize efficiency of such an FEL is discussed. A numerical simulation s howed that the efficiency of an EEL on a slow cyclotron wave with tape red wiggler field could reach the 25% level, thus demonstrating the po tential of that FEL to compete with other sources of coherent microwav es. Features of nonlinear regime are discussed and results of numerica l simulation are presented.