Phase Locking in Backward-Wave Oscillators with Strong End Reflections

Summary form only given. At present, there is a strong interest in the development of plasma-assisted slow-wave oscillators (pasotrons), which can be configured as either backward-wave oscillators or amplifiers. This interest is stimulated by the fact that in pasotrons electron beams are produced by plasma guns and the beam transport is provided by ion focusing. Correspondingly, these devices can operate without guiding magnetic fields, which usually require heavy and bulky magnets or solenoids. The absence of heavy magnets makes pasotrons very attractive for various airborne and field applications. At present, L-band pasotron oscillators can operate with efficiencies exceeding 50% and deliver the output power in excess of 1 MW and the microwave energy of more than 1 kJ per pulse. For some applications, it is desirable to control the phase of outgoing radiation. This fact has stimulated our interest in the analysis of phase-locked operation of the pasotron backward-wave oscillator. Results of this analysis was reported in this paper. First, it is shown that the use of a prebunched beam allows one to increase the device efficiency from the maximum slightly exceeding 30% in the case of free-running operation to the values exceeding 50% at large enough bunching parameters. Then, we present some results of the study of the pasotron phase-locked operation. In particular, it is shown that the locking bandwidth of the device can be about two times larger than the width of the cavity resonance. Finally, we discuss the applicability of our results to possible experimental configurations.