Instabilités rayonées dans un plasma par un faisceau d'électrons.

The note attempts to explain a continuous type of emission observed (Kellog et al., 1975) in experiments in which electron beams are injected into the ionosphere, in terms of quasi-electrostatic waves radiated by the beam and observable at large radial distances. A BKW approximation for solving the wave potential is worked out for boundary conditions such that waves radiated by the beam have a positive group velocity at large values of r, the distance from the beam. A constant-density, thin beam is assumed, and attention is restricted to waves of azimuthal symmetry and frequency below the electron cyclotron frequency. The solutions indicate that the wave properties are very sensitive to injection characteristics and beam neutralization, in qualitative accord with experimental evidence.