Electromagnetic Emission Driven by Electron Beam Instability in the Jovian Polar Regions

Upward energetic electron beams are often observed simultaneously with the plasma-wave emission in the Jovian polar regions, where the electron cyclotron frequency omega(pe) is much larger than the plasma frequency omega(pe). This study gives a comprehensive wave and instability analysis in the extreme plasma environment with omega(pe) >> (pi e) . We find that energetic electron beams can effectively drive the electron acoustic/magnetoacoustic instability. The excited electron acoustic/magnetoacoustic waves distribute from the parallel direction to the highly oblique direction, and their wave frequencies are always below the plasma frequency. These waves are electrostatic at parallel propagation, and exhibit electromagnetic polarization at oblique propagation. These theoretical predictions are qualitatively consistent with the main observed features of electromagnetic fluctuations in the Jovian polar regions. Therefore, we propose that upward electron beam-driven electron acoustic/magnetoacoustic waves can contribute to the plasma-wave emission in Jupiter's polar environments. Furthermore, energetic electron beam-driven electron acoustic/magnetoacoustic waves may exist in Saturn's polar regions and solar flare loops, where the extreme plasma condition omega(ce) >> omega(pe) is satisfied in these plasma environments.