RELATIVISTIC BACKWARD-WAVE OSCILLATORS OPERATING NEAR CYCLOTRON-RESONANCE

Microwave sources based on backward-wave oscillators (BWO's) driven by relativistic electron beams are capable of producing high-power coher ent radiation in the cm and mm wavelength region. When the axial magne tic field used in these devices to confine the electron beam satisfies the condition of cyclotron resonance there is a significant modificat ion in the behavior of BWO due to beam coupling to cyclotron modes. In this paper a time-dependent, self-consistent theory of BWO's is devel oped, taking into account a possible cyclotron interaction. The analys is of the system near the cyclotron resonance yields the power drop du e to the cyclotron absorption effect observed in many BWO experiments. In addition, the theory predicts that there exists a region of magnet ic field strength, where an increase in power and efficiency is possib le. Depending on the value of the magnetic field and beam coupling to cyclotron mode various regimes of BWO operation are possible, includin g stable single-frequency oscillations, self-modulation, and a success ion of microwave bursts.