Coherent spontaneous emission from a modulated beam injected in a magnetized plasma

Abstract

The linear stage of the coherent emission of a modulated beam injected in a cold plasma is investigated. The feature of the radiation produced is shown to be governed by the ratio ω2p/ω2c of the background plasma. This kind of emission provides an efficient way to convert the kinetic energy of the beam particles into electromagnetic wave energy: The power given to waves averaged over periods of the beam modulation is found to be an appreciable part of the initial beam power. The transfer can be maximized in the electron whistler range (Cerenkov emission) for electron beams whose characteristics are designed to met the ‘‘focalization condition’’ (double pole in the dispersion relation). The most suitable mode is the normal Doppler shift ion cyclotron mode for ion beams. Application to relevant ionospheric plasmas is considered.