Theory of cyclotron superradiance from a moving electron bunch under group synchronism conditions

A theory is presented of cyclotron superradiance from an electron bunch rotating in a uniform magnetic field and drifting at a velocity close to the group velocity of a wave propagating in a waveguide. It is shown that, in a comoving frame of reference, the bunch emits radiation at a frequency close to the cutoff frequency of the waveguide. Superradiance implies the azimuthal self-bunching of electrons, which is accompanied by coherent emission of the stored rotational energy in a short electromagnetic pulse. Linear and nonlinear stages of the process are analyzed. The growth rate of the superradiance instability is determined. It is shown that the maximum growth rate is attained under group synchronism conditions. The peak power and the characteristic duration of the cyclotron superradiance pulse are determined by numerical simulation. The characteristic features of the superradiance pulses are described in the comoving and laboratory frames. The results of theoretical analysis are compared with experimental data.