Resonant Cyclotron Emission of Whistler Waves by a Modulated Electron Beam

The first observations of whistlers excited spontaneously by a modulated electron beam through normal Doppler shifted resonance have been reported in a laboratory experiment. The excited waves are propagating opposite to the beam direction and their phase and group velocities are characteristic of beam-whistler resonant cyclotron coupling. These results should shed light on mechanisms of whistler waves excitation in space plasmas, either by artificial beams injected from spacecraft in the ionosphere and the magnetosphere or by fluxes of energetic particles present in many astrophysical and space phenomena.