Cyclotron effects in relativistic backward wave oscillators

Summary form only given, as follows. The operation of high power Cherenkov devices such as backward wave oscillators is based on the interaction of high current, relativistic electron beams with synchronous electromagnetic fields of periodically corrugated waveguides. The high current electron beam is guided by a strong axial magnetic field. Therefore, in addition to the Cherenkov synchronism, the cyclotron resonance conditions can be realized for different spatial harmonics of both forward and backward waves. The cyclotron interaction manifests itself in the output power dependence on the axial focusing magnetic field. We developed linear and nonlinear theories that predict this dependence and the results from the numerical modeling compared favourably with the existing experimental data. We also found that the combined Cherenkov and cyclotron interaction may result in a higher efficiency conversion of the electron beam energy into radiation.