Kinetic aspects of the ion current layer in a reconnection outflow exhaust

TL;DR

This study uses 2D particle-in-cell simulations to analyze the kinetic behavior of ions in the current layer during magnetic reconnection, revealing complex ion populations and demonstrating trapped ion orbits as potential observational signatures.

Contribution

It provides new insights into ion dynamics and orbit structures in reconnection outflows through self-consistent PIC simulations.

Findings

Ion current layer contains multiple ion populations.

Trapped ions exhibit regular orbits in chaotic dynamics.

Ion fluid is nonideal, sub-Alfvenic, and nondissipative.

Abstract

Kinetic aspects of the ion current layer at the center of a reconnection outflow exhaust near the X-type region are investigated by a two-dimensional particle-in-cell (PIC) simulation. The layer consists of magnetized electrons and unmagnetized ions that carry a perpendicular electric current. The ion fluid appears to be nonideal, sub-Alfvenic, and nondissipative. The ion velocity distribution functions contain multiple populations such as global Speiser ions, local Speiser ions, and trapped ions. The particle motion of the local Speiser ions in an appropriately rotated coordinate system explains the ion fluid properties very well. The trapped ions are the first demonstration of the regular orbits in the chaotic particle dynamics [Chen and Palmadesso, J. Geophys. Res., 91, 1499 (1986)] in self-consistent PIC simulations. They would be observational signatures in the ion current layer near reconnection sites.