Whistler wave emission by a modulated electron beam through transition radiation

Measurements have been performed in a laboratory experiment modeling the interaction of a modulated electron beam with a magnetized plasma under conditions relevant to space experiments involving beam injection. Both whistler emission through Cherenkov resonance and a nonresonant mechanism of transition radiation from the point of beam injection into the plasma have been observed. Electrons injected from the gun into the plasma pass from one medium (gun chamber) into another (plasma volume) and electromagnetic fields change as charges cross the metallic interface between both media, giving rise to transition radiation. This type of beam radiation, observed separately from the resonant Cherenkov emission owing to adequate choices of the physical conditions, has been characterized as a function of the beam and plasma parameters. Moreover, in the case of beams injected from satellites in the ionospheric and magnetospheric plasmas, this nonresonant emission, mainly located in the near gun region, can be governed by an adequate control of the radiator parameters and separated from resonant emissions. (C) 1999 American Institute of Physics. [S1070-664X(99)03905-1].