Resonant instabilities of kinetic Alfvén waves in the Earth's magnetosphere with superthermal electrons

Abstract

A theoretical plasma model for the generation of kinetic Alfvén waves (KAWs), having background Maxwellian ions, κ-electrons, and drifting Maxwellian beam ions, is discussed. The ion beam streams along the ambient magnetic field, whereas velocity shear is perpendicular to it. The role played by nonthermal electrons in the excitation of resonant KAWs with the velocity shear in the ion beam as the free energy source is examined. In the presence of κ-electrons, the effect of plasma parameters such as propagation angle, ion beam temperature, number density, and ion plasma βi on the growth of the KAWs is analyzed. It is found that nonthermal electrons restrict the excitation of KAWs by reducing the growth rate of the waves. It is inferred that a high velocity shear and ion beam density are required to excite KAWs in the presence of nonthermal electrons. The model is capable of producing waves with frequencies up to ≈18 mHz in the auroral region of Earth's magnetosphere.