Kinetic Alfvén waves generated by ion beam and velocity shear in the Earth's magnetosphere

Abstract

Generation of Kinetic Alfvén Waves (KAWs) in a generalized three component plasma model consisting of the background cold ions, hot electrons, and hot ion beams, where all the three species have non-uniform streaming and velocity shear, is discussed. First, the role played by the ion beam solely in exciting KAWs is analyzed. Next, how this behavior gets modified when the velocity shear is present along with the streaming ion beam is discussed. The effects of other parameters such as temperature, number density, and propagation angle on the growth of KAWs are explored. It is found that when shear is positive and ions are streaming along the ambient magnetic field, KAWs are stabilized. On the other hand, with positive shear and an anti-parallel ion beam or vice-versa, KAWs with a larger growth rate are excited as compared to the case of waves excited by the ion beam alone. Also, for the first time, we have shown the combined effect of the ion beam and velocity shear on the generation of KAWs. The theoretical model can generate ultra-low frequency waves with frequencies up to ≈60 mHz for the plasma parameters relevant to auroral/polar cusp field lines.