A possible mechanism for the formation of filamentous structures in magnetoplasmas by kinetic Alfven waves

Due to having strong anisotropy in their polarization state and spatial structure, it is believed that kinetic Alfven 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 (R) and the growth rate (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 k(0)(-1), while the growth rate of KAWs has a maximum in the growing ranges of k(0)(-1). On the other hand, the excited KAWs are weakly dispersive with (e)k(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.