Electromagnetic Emissions in the Ionosphere‐Pulsed Electron Beam System

Abstract

Numerous rocket and satellite projects were devoted to study of astrophysical plasma with the aid of active electron beam experiments. The quality and volume of wave data from such experiments did not fulfill original expectations due to complexity of involved processes, technical malfunctions and limited diagnostic. There were several cases when pulsed electron beam had been injected from the APEX satellite into an otherwise unmodified ionospheric plasma. Diversely structured beam induced emissions were registered. In many cases, a very prominent doublet could be convincingly identified as an upper hybrid band. Those spectra with sharp peaks below electron gyroharmonics were successfully resolved in the framework of cold plasma - diluted weakly relativistic beam system. Electromagnetic X, O, Z mode emissions relevant for astrophysical applications were identified. The identification procedure, characteristic spectra and experimental conditions are discussed. Reproducibility of distinct spectral features and their sensitive dependence on the ratio f n /f c of ambient plasma f n and gyro f c frequencies support the concept of simulation of astrophysical plasmas in active experiments. Controlled creation of such environments along low altitude orbits provides opportunity for evaluation and development of measurement techniques.