Improved Efficiency of Backward-Wave Oscillator With an Inclined Electron Beam

The possibility of the efficient operation of a backward-wave oscillator (BWO) with an electron beam inclined with respect to the surface of a periodic structure-a clinotron-is analyzed here. The beam inclination provides the possibility of effective interaction by all particles of a thick electron beam with the slow evanescent harmonic of the cavity modes. The problem of electron-beam-wave interaction is treated in a self-consistent formulation. A theoretical analysis shows that the inclination of the electron beam to the grating surface decreases the demand of the clinotron for magnetic field magnitude and beam velocity spread compared to a conventional BWO. It is demonstrated that, for an optimal inclination angle and an optimal beam thickness, the clinotron efficiency exceeds the efficiency of a conventional BWO considerably given the same electron beam parameters. The developed multimode theory results are in satisfactory agreement with the theory of a BWO in terms of reflections and particle-in-cell simulations.