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.
A resonant instability of kinetic Alfvén waves (KAWs) driven by ion beam is discussed through a theoretical model encompassing Maxwellian background ions and beam ions and non-Maxwellian κ-electrons. The ion beam velocity alone as a source is able to excite the KAWs up to a significant growth. The non-Maxwellian parameter κ impedes the growth of KAWs by restricting the wave unstable region. The effects of other plasma parameters such as propagation angle, temperature of the plasma species, and ion plasma beta on the excitation of KAWs are also examined. The present model can generate waves with frequencies in the range of ≈6.6–51.2 mHz, which are relevant to explaining the observed ultralow frequency waves at auroral ionospheric altitudes. Theoretical model predictions will also be applicable to other planetary environments where ion beams and non-Maxwellian κ-electrons are present.
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.
A nonresonant instability of kinetic Alfvén waves (KAWs) is studied in a three-component plasma system consisting of background cold ions, an ion beam, and hot electrons with a κ-distribution. The nonresonant KAW instability is produced by the combined sources of ion beam and velocity shear. It is found that the wave excitation by velocity shear alone will give rise to purely growing KAWs, whereas the ion beam velocity alone as a source cannot excite the waves for the considered plasma parameters. It is also observed that the combined sources of ion beam and velocity shear can excite the KAWs in nonresonant instability with finite wave frequency (the mode is not a purely growing mode). Also note that κ-electrons restrict the wave propagation very close to 90°, whereas the Maxwellian electrons permit the wave to propagate a few degrees away from 90°. It is inferred that the presence of κ-electrons shrinks the wave-unstable region of a KAW’s nonresonant instability. The coupling between KAWs and ion-acoustic waves occurs at a lower value of β i for Maxwellian electrons as compared to κ-electrons.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations –citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.