Magnetic Island Structures Associated with Kinetic Alfvén Solitary Wave in Two-fluid Plasma

Abstract

We investigate the formation of magnetic islands and the onset of tearing instability within kinetic Alfvén solitary waves in a two-fluid space plasma. These localized structures, featuring internal magnetic shear, naturally support magnetic reconnection processes analogous to tearing modes in magnetically confined fusion plasmas. Treating the solitary wave as a quasi-static background equilibrium, we analyze the resulting topological modifications by making use of the magnetic flux function, in analogy with tokamak plasmas. We find that the spatial size of the magnetic island scales with the square root of the magnetic flux perturbation. Introducing the tearing stability index , we derive the growth rate of the tearing mode using a resistive magnetohydrodynamic framework. Our analysis reveals that tearing modes grow only when the mode’s wavenumber exceeds the inhomogeneity scale, becoming marginally stable when the two are comparable. The emergence of magnetic islands has significant implications for cross-field particle transport, turbulence, and acceleration. In particular, the electron diffusion across magnetic fields may be governed by the island size rather than the Larmor radius, potentially accounting for anomalous transport. Furthermore, in certain regimes, unbounded island growth may signal the collapse of the solitary wave structure, enabling a large-scale transfer of magnetic energy to particle energy. These results suggest a unifying mechanism connecting magnetic reconnection in space plasmas with tearing instabilities in laboratory fusion plasmas.