Free electron maser experiments based on a coaxial 2D Bragg cavity

The generation of high power microwave radiation from a two-dimensional (2D) Bragg co-axial free electron maser (FEM) is reported. Two 2D Bragg structures positioned at the input and output of an oversized coaxial interaction region were used to define the cavity of the FEM. Measurements of the transmission coefficient of the 2D Bragg structures were conducted with experimental results compared with theoretical predictions. A 1 kA, 475 kV annular electron beam of a diameter of 7 cm was measured. The frequency of the microwave radiation generated, was measured to lie within the reflection zone of the 2D Bragg cavity.