A possiblemechanism for the formation of filamentous structures inmagnetoplasmas by kinetic Alfvén waves

摘要

Due to having strong anisotropy in their polarization state and spatial structure, it is believed that kinetic Alfvén waves (KAWs) can play an important role in various energization phenomena of plasma particles and the fine-structure formation in magnetoplasma environments. The filamentous fine structures are a kind of the common density inhomogeneity phenomena in magnetoplasmas, and hence, the density gradient is one of the sources of free energy that can lead to KAWs instabilities. In this paper, based on the two-fluid model in which ions and electrons are treated as separate fluids, we investigate the effect of density gradient inhomogeneous on the dispersion and instability of KAWs in a magnetoplasma. The results show that KAW instability can be excited effectively by the density gradient. Especially, both the real frequency ω_R and the growth rate ω_I of KAWs are dramatically dependent on the spatial position x in the presence of an inhomogeneous density gradient. The results also show that the real frequency increases with the characteristic spatial scale of inhomogeneity κ_0~(?1), while the growth rate of KAWs has a maximum in the growing ranges of κ_0~(?1). On the other hand, the excited KAWs are weakly dispersive with λ_ek_x < 1. The results have potential importance for a better understanding of the microphysics of the filamentous fine-structure formation since the phenomena of density gradient inhomogeneous are ubiquitous in various magnetoplasmas, such as in the laboratory plasma as well as in both the solar coronal and terrestrial auroral plasmas.