The Properties And Generation Of Electromagnetic Ion Cyclotron Waves In Earth Space H~+-He~+-O~+ Plasmas

Electromagnetic ion cyclotron (EMIC) waves are natural plasma emissions in the Earth's magnetosphere. These waves play important roles in the magnetosphere, e.g., leading to the fast pitch angle scattering loss of radiation belt electrons. Although previous studies have explored several important features of EMIC waves affected by heavy ions, there still lacks a comprehensive study for EMIC waves in multi-component plasmas including heavy ions such as He+ and O+.This thesis investigates the properties and excitations of EMIC waves in space H~+-He~+-O~+ plasmas, focusing on the roles of heavy He+ and O+ ions. Firstly, by cold four-fluid theory, we obtained the complete analytical expressions of dispersion equations and polarizations of EMIC waves as well as a right-hand polarized mode wave, and analyzed the wave properties at different propagation angles in cold H~+-He~+-O~+ and +-He+-O- plasmas. Secondly, on the basis of the hot four-fluid theory, we found the new analytic expressions of the dispersion relation, cut-off and resonance frequency of parallel-propagating EMIC wave in the presence of the anisotropic thermal pressures. By combining kinetic and fluid models,we explored the effects of plasma thermal pressures on the properties and growth of EMIC waves.Lastly, the obliquely propagating EMIC waves are studied in hot four-component plasma.The main results are summarized as follows:(1) In cold H~+-He~+-O~+ plasmas,The presence of heavier He+ and O+ ions lead to the multi-band structure of EMIC waves and two stop band where the left-hand wave can not propagate. The obvious changes of the electric polarization occur at the two crossover frequencies and the wave number range corresponding to the linear polarization will gradually broaden with increasing the propagation angle.(2) In H~+-He~+-O~- plasmas, there are two stop bands and only one crossover frequency in comparison with two crossover frequencies in cold H~+-He~+-O~+ plasma.The stop band for right-hand polarized wave corresponds to the frequency range between the resonance frequency in He+ band and the cutoff frequency in O" band;and the stop band for left-hand polarized wave corresponds to the frequency range between the resonance frequency in He+ band and the cutoff frequency in H+ band.(3)Hot and anisotropic heavy ions may suppress completely the growth of He+band EMIC waves, whereas H+ band waves are growing no matter heavy ions are cool or hot. At large O+ ion concentration, O+ band waves will grow considerably as hot proton and heavy ions are anisotropic.(4) Anisotropic thermal pressures of heavy ions result in the resonance frequency of EMIC waves that is larger than that given by the cold fluid model. They narrow the corresponding stop-bands. Furthermore, the anisotropic ion thermal pressures lead to the minimum resonant energy of electrons interacted with EMIC waves have frequencies higher than that predicted by the cold fluid model.