CERENKOV EMISSIONS OF ION ACOUSTIC-LIKE WAVES GENERATED BY ELECTRON-BEAMS EMITTED DURING TSS 1R

During the Tethered Satellite System reflight the Spacecraft Particle Correlation Experiment detected fluxes of energetic electrons and ions that were simultaneously modulated at low frequencies during firings of both the fast pulsed electron gun (FPEG) and the electron generator assembly (EGA). The modulations have been interpreted as signatures o f large-amplitude, ion acoustic-like waves excited in Cerenkov interac tions between electron beams and ambient plasmas as the shuttle moved at supersonic speeds across the ionospheric magnetic field. We present examples of particle modulations observed during steady beam emission s. Measurements show that (1) most electron modulations were at freque ncies of several hundred Hertz and (2) ions modulated at similar frequ encies appeared at spectral energy peaks during shuttle negative charg ing events. Detection of modulated ion fluxes confirms the Cerenkov em ission hypothesis. Observed frequency variations indicate that the EGA beam underwent more spatial spreading than the FPEG beam.