Influence of Oxygen Ions on the Structure of the Thin Current Sheet in the Earth’s Magnetotail

Abstract

During geomagnetic substorms, the current sheet in the Earth’s magnetotail can transversely reduce in thickness from a few radii of the Earth (RE) to one to several proton gyroradii, 250–2000 km. It is the key structure in which the energy of the magnetic field is stored and later released due to the development of instability and magnetic reconnection during the substorm period. Despite its small thickness, the thin current sheet has a complex multiscale structure with a hierarchy of embedded layers that determines its properties. During substorms, single-charged oxygen ions enter the Earth’s magnetotail from the ionosphere and their concentrations can be comparable to those of protons. The interaction of oxygen ions with the current sheet, which results in changes in its structure and properties, is not well studied. The self-consistent profiles of the magnetic field, current densities, and plasma in the multicomponent magnetotail plasma are analyzed in a wide range of system parameters within the hybrid model of the quasi-equilibrium current sheet. It is shown that the current sheet is a multiscale structure embedded in a wide plasma layer. The increase in the concentration of oxygen ions in the current sheet leads to its thickening and formation of additional embedded scale. At the same time, breaks characterizing the transition from the oxygen-ion dominated region in the current sheet to the proton- and electron-dominated region appear on the profiles of the magnetic field and current density. The amplitude of the current density of such an embedded layer decreases in proportion to the concentration of oxygen ions. The dependence of the embedding parameter on relative concentrations of heavy ions, as well as their thermal and drift velocities, is studied.