2D Bragg high power microwave source driven by an annular electron beam

The use of two dimensional distributed feedback has been proposed as a method of producing spatially coherent radiation from a large size relativistic electron beam of either sheet or annular geometry. In this scheme it is possible to increase the total beam power and, correspondingly, the microwave power while still keeping the current and radiation density constant. The new feedback mechanism allowing effective mode selection in an oversized cavity can be realised in planar and coaxial 2D Bragg cavities with double periodical corrugation of the walls. Mutual scattering on this corrugation of the electromagnetic energy fluxes propagating in the forward, the backward and transverse directions (relative to the direction of the electron beam propagation) takes place. The additional transverse electromagnetic energy fluxes synchronize the radiation from different parts of a large size annular electron beam. In this paper both the experimental cold microwave measurements and numerical results are presented. A comparison was made between the novel 2D Bragg mirror and a conventional 1D Bragg mirror. The design of the Strathclyde free electron maser with a coaxial 2D Bragg resonator based on 2D and 1D mirrors and driven by an oversized annular electron beam is presented.