Self-consistent model of 1D current sheet: The role of drift, magnetization and diamagnetic currents

Abstract

Thin anisotropic current sheets are important elements of the magnetospheric dynamics and structure. We develop an analytical theory of the self-consistent current sheet (CS) created by the ion streams impinging from the plasma mantle. The nonlocal analogue of the Grad-Shafranov equation is obtained and numerically solved in the quasi-adiabatic approximation, i.e. neglecting jumps of the sheet adiabatic invariant I z which is possible when the minimum curvature radius of the magnetic field is less than the thermal ion gyroradius. General solutions allow to consider both the cases of strong and weak anisotropy. Resulting self-consistent current is a sum of the drift cyclotron and magnetization currents flowing in opposite directions. In the immediate vicinity of the neutral plane the paramagnetic current arising from the meandering motion of ions on Speiser orbits becomes dominating. The maximum CS thickness is achieved in the case of weak plasma anisotropy and is of the order of the thermal ion gyroradius outside the sheet. Separately the CSs with nonadiabatic ions are considered, where the jumps of I z become essential. For that case of the so called superstrong anisotropy, when the ratio of the drift velocity outside CS to the thermal ion velocity exceeds the ratio of the magnetic field outside CS to its value inside CS (v D /v T > B 0 /B n ), the assessment of the CS thickness is also performed. It is found in particular that the CS thickness can be reduced down only up to some finite value, which depends upon the parameter B n /B 0 . The model predicts essential reduction of the CS thickness under the influence of the convection electric field, which might have important implications for the substorm dynamics.