A comprehensive model for the kinetic Alfvén waves in space and astrophysical plasmas

Abstract:

A comprehensive theoretical model is developed to study the excitation of kinetic Alfvén waves (KAWs) in space and astrophysical plasmas. This model considers a few significant sources of free energy, such as velocity shear, temperature anisotropy, and beams of the plasma species for the excitation of KAWs in a non-Maxwellian κ-distributed plasma environment. The results for the Maxwellian distributed plasma system can be obtained from the non-Maxwellian distribution in the limit κ→∞.The model has vast applications in the prospective of space and astrophysical plasmas as the mentioned free energy sources are available in the solar wind and solar atmosphere, and in different regions of the Earth’s magnetosphere. To show the significance of the model, a few three component theoretical models, that are deduced from the comprehensive model, are discussed. The first one considers the background ions, electrons and beam ions in a Maxwellian distributed plasma species to study the generation of KAWs for both the resonant and nonresonant cases. In appropriate limits, the results match with Lakhina [2008]. The second one deals with the excitation of KAWs by ion beam and velocity shear for a three component plasma model with non-Maxwellian electrons and the background ions and beam ions with Maxwellian distribution. The obtained results go over to those of Barik et al. [2019] under the same limits. The effect of temperature anisotropy on the excitation of KAWs is also discussed. The comprehensive model may be utilized to deduce the characteristics of KAWs in presence of different free energy sources and it may explain some of the observed features of the ultra-low frequency (ULF) waves in the Earth’s magnetosphere.

References:

1. Lakhina, G. S. "Generation of kinetic Alfvén waves by velocity shear instability on auroral field lines." Advances in Space Research10 (2008): 1688-1694.
2. Barik, K. C., S. V. Singh, and G. S. Lakhina. "Resonant instabilities of kinetic Alfvén waves in the Earth's magnetosphere with superthermal electrons." Physics of Plasmas11 (2019): 112108.