Beam of neutral or charged atoms as a source of stimulated microwave radiation

High-frequency electromagnetic dynamics of charged or neutral atom beams which are widely used at present is analyzed. One of perspective mechanisms of radiation bound with high-frequency intratomic electronic transitions is considered. As it is shown a flux of fast nonexcited atoms, due to anomalous Doppler´s transitions on slow waves in a gas or plasma, can be unstable and be a source of stimulated high-frequency radiation. As a whole process has a complex nature since photon radiation is accompanied by excitation of atoms with following emission of more high-frequency photons. The possible parameters of such physical systems are estimated