A comparative study of ion beam and velocity shear driven resonant instability of kinetic Alfve´n waves with j-electrons

Abstract

Acomparative analysis is carried out between the ion beam and velocity shear as the possible source of free energy in the generation of kinetic Alfve ´n waves (KAWs) through a three-component theoretical model. The model consists of Kappa electrons, Maxwellian background ions, and drifting-Maxwellian beam ions as the constituent species. The ion beam and velocity shear-driven resonant instabilities of KAWs are investigated and the results are compared on a one-to-one basis. In the presence of j-electrons, velocity shear is found to be a more effective source of free energy as compared to ion beam in the generation of KAWs. The threshold value of both energy sources in the excitation of KAWs is found numerically for a fixed set of plasma parameters. The characteristics of KAWs such as real frequency, parallel and perpendicular wavelength range, wave unstable region, growth rate, etc. are examined for both cases and the results are compared with the observed values relevant to Earth’s magnetotail.