Ion Temperature Anisotropy Limits from Magnetic Curvature Scattering in Magnetotail Reconnection Jets

TL;DR

This paper investigates how magnetic curvature scattering constrains ion temperature anisotropy in Earth's magnetotail, using analytical models, spacecraft data, and simulations to understand current sheet stability in collisionless plasmas.

Contribution

It provides the first analytical thresholds for ion anisotropy limits due to curvature scattering in a magnetotail-like configuration, validated by observations and simulations.

Findings

Curvature scattering limits ion temperature anisotropy in the magnetotail.

Analytical thresholds match spacecraft observations.

Stability of the current sheet is maintained by these anisotropy limits.

Abstract

In collisionless plasmas, relaxation of the deviations of ion velocity distribution functions (VDFs) from local thermodynamic equilibrium occurs through particle interactions with electromagnetic fields. In particular, in the Earth's magnetotail, the deviations of the ion VDFs, typically consisting of multiple components, from the equilibrium must be limited to maintain stability of the current sheet. Curvature scattering is a leading candidate mechanism to limit such deviations, but its role remains insufficiently understood. We investigate the limits of ion temperature anisotropy in a magnetotail-like configuration by modeling a quasi-1D current sheet with a finite magnetic field curvature and three ion populations. We derive analytical thresholds for anisotropy based on current sheet stability and validate against spacecraft observations and numerical simulations. Our findings demonstrate that curvature scattering imposes limits on ion anisotropies, thereby maintaining the stability of the current sheet.