Precipitation of highly energetic protons by helium branch electromagnetic ion cyclotron triggered emissions

Abstract

In the equatorial region of the Earth's inner magnetosphere, the electromagnetic ion cyclotron (EMIC) triggered emissions are generated through interaction with energetic protons. We investigate the generation process of the EMIC triggered emissions in the He⁺branch and associated precipitation of the energetic protons using a one-dimensional hybrid simulation with a cylindrical parabolic magnetic geometry. The simulation results show a good agreement with the nonlinear wave growth theory. As the electron density becomes higher as in the plasmasphere or the plasmaplume, the wave amplitude thresholds for both H⁺ and He⁺ band triggered emissions become lower and their nonlinear growth rates become higher. The higher hot proton density also makes the thresholds lower. While the H⁺ branch triggered emissions interact with a few keV protons, the He⁺ branch triggered emissions interact with more energetic protons of a few hundred keV with a larger nonlinear growth rate.