The controlling effect of ion temperature on EMIC wave excitation and scattering

TLDR

The study investigates the dispersion relation of parallel propagating EMIC waves in a magnetized homogeneous plasma of hot H⁺ and He⁺ ions. The authors analyze this dispersion relation and use the maximum wavenumber of unstable L‑mode waves to determine the plasma conditions required for EMIC wave scattering of MeV electrons. Hot plasma effects of He⁺ and H⁺ significantly modify the cold plasma dispersion relation near ΩHe⁺, potentially eliminating the stop band above ΩHe⁺ and rendering waves near ΩHe⁺ unstable; the study concludes that extreme conditions (ωpe/|Ωe| ≳ 25 and H⁺ anisotropy > 1) are needed for resonance with 1 MeV electrons, limiting such scattering to the inner plasmasphere or storm‑time plumes.

Abstract

[1] The dispersion relation of parallel propagating EMIC waves is investigated in a magnetized homogeneous plasma consisting of hot H+ and He+ ions. We demonstrate that the hot plasma effects associated with He+ and H+ significantly modify the cold plasma dispersion relation, especially near ΩHe+. For plasmas with a sufficiently small fraction of warm He+ and a sufficiently dense, hot and anisotropic H+ population, the cold plasma stop band above ΩHe+ may vanish, and waves near ΩHe+ may be unstable. The maximum wavenumber for unstable L-mode waves due to the hot plasma modification is used to identify the plasma conditions required for EMIC wave scattering of MeV electrons. We conclude that relatively extreme conditions (ωpe/|Ωe| > ∼25, and H+ anisotropy >1) are required for resonance with electrons near 1 MeV, which limits such scattering only to the region just inside the plasmasphere or storm time plumes.