THEORY OF RELATIVISTIC CYCLOTRON MASERS

In this paper we have made an attempt to review the present status of the theory of cyclotron masers with relativistic electron beams. After discussing the basic features of electron-cyclotron radiation under c onditions of normal and anomalous Doppler frequency shifts, we conside r particle deceleration by a constant amplitude electromagnetic wave i n a constant magnetic field using the formalism developed earlier for cyclotron autoresonance acceleration of electrons. An optimal cyclotro n resonance mismatch was found that corresponds to the possibility of complete deceleration of relativistic electrons. Then, interaction of relativistic electrons with resonator fields is considered and the eff iciency increase due to electron prebunching is demonstrated in a simp le model. Since an efficient interaction of relativistic electrons wit h the large amplitude electromagnetic field of a resonator occurs at a short distance, where electrons make a small number of electron orbit s, the issue of the simultaneous interaction of electrons with the fie ld at several cyclotron harmonics is discussed. Finally, we consider d eceleration of a prebunched electron beam by a traveling electromagnet ic wave in a tapered magnetic field. This simple modeling is illustrat ed with a number of simulations of relativistic gyroklystrons and gyro twistrons (gyrodevices in which the bunching cavity of the gyroklystro n is combined with the output waveguide of the gyro-traveling-wave-tub e).