Free-electron maser based on two-dimensional distributed feedback

The study of a co-axial Free-Electron Maser (FEM) based on 2D and 1D distributed feedback and driven by a large diameter (70mm), annular electron beam is presented. It has been demonstrated that 2D distributed feedback in the input mirror allowed 8mm radiation emitted from different parts of the oversized electron beam to be synchronized. The FEM operating in the (35.9GHz to 38.9GHz.) frequency region generated 60MW, 150ns duration millimetre wave pulses which contained ∼9J of energy in the pulse. Good agreement between theoretical predictions and experimental data is demonstrated