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Upward energetic electron beams are often observed simultaneously with the plasma-wave emission in the Jovian polar regions, where the electron cyclotron frequency Ωce is much larger than the plasma frequency ωpe. This study gives a comprehensive wave and instability analysis in the extreme plasma environment with Ωce ≫ ωpe. 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 Ωce ≫ ωpe is satisfied in these plasma environments. [ABSTRACT FROM AUTHOR]

Electron temperature anisotropies and electron beams are nonthermal features of the observed nonequilibrium electron velocity distributions in the solar wind. In collision-poor plasmas these nonequilibrium distributions are expected to be regulated by kinetic instabilities through wave–particle interactions. This study considers electron instabilities driven by the interplay of core electron temperature anisotropies and the electron beam, and first gives a comprehensive analysis of instabilities in arbitrary directions to the background magnetic field. It clarifies the dominant parameter regime (e.g., parallel core electron plasma beta , core electron temperature anisotropy , and electron beam velocity Veb) for each kind of electron instability (e.g., the electron beam-driven electron acoustic/magnetoacoustic instability, the electron beam-driven whistler instability, the electromagnetic electron cyclotron instability, the electron mirror instability, the electron firehose instability, and the ordinary-mode instability). It finds that the electron beam can destabilize electron acoustic/magnetoacoustic waves in the low- regime, and whistler waves in the medium- and large- regime. It also finds that a new oblique fast-magnetosonic/whistler instability is driven by the electron beam with in a regime where and Aec < 1. Moreover, this study presents electromagnetic responses of each kind of electron instability. These results provide a comprehensive overview for electron instability constraints on core electron temperature anisotropies and electron beams in the solar wind. [ABSTRACT FROM AUTHOR]