Whistler wave emission by a modulated electron beam through transition radiation

Measurements have been performed in a laboratory experiment modeling the in teraction of a modulated electron beam with a magnetized plasma under condi tions relevant to space experiments involving beam injection. Both whistler emission through Cherenkov resonance and a nonresonant mechanism of transi tion radiation from the point of beam injection into the plasma have been o bserved. Electrons injected from the gun into the plasma pass from one medi um (gun chamber) into another (plasma volume) and electromagnetic fields ch ange as charges cross the metallic interface between both media, giving ris e to transition radiation. This type of beam radiation, observed separately from the resonant Cherenkov emission owing to adequate choices of the phys ical conditions, has been characterized as a function of the beam and plasm a parameters. Moreover, in the case of beams injected from satellites in th e 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 Ame rican Institute of Physics. [S1070-664X(99)03905-1].