EFFECTS OF ARTIFICIALLY INJECTED ELECTRON-BEAMS ON THE CHARACTERISTICS OF GROUND VLF TRANSMITTER SIGNALS IN THE IONOSPHERE

Spectral broadening of signals from a ground-based VLF transmitter was observed onboard the Magion-3 sub-satellite during electron beam inje ction from the Intercosmos-25 (APEX) satellite. Broadening of the orde r of 300-500 Hz was apparently correlated with the 2 s-periodic sequen ce of the electron gun pulses which were modulated in amplitude with f requencies 30.5 < f(m) < 31,250 Hz. No effects were found for those el ectron gun pulses with f(m) = 62.5, 125 and 250 kHz. The observations were made in the middle latitude ionosphere st altitudes between 1175 and 1580 km; the distance between satellite and sub-satellite was abou t 250 km. The electron gun current and the energy of electrons were 10 0 mA and 10 keV, respectively, and the duration of the elementary puls e of current was 2 mu s. The data are interpreted in terms of the scat tering of whistler mode waves into quasi-electrostatic waves by period ic small-scale plasma inhomogeneities or ELF plasma turbulence created by the pulse-modulated electron beam in the ionosphere.