Collisionless magnetic reconnection in the presence of a guide field

TLDR

A range of guide fields is studied in Harris current sheets using both implicit and explicit particle‑in‑cell simulations with mass ratios up to the physical value to explore reconnection across different β regimes. The simulations reveal that the reconnection rate decreases with increasing guide field, depends weakly on mass ratio, and that off‑diagonal electron pressure tensor components break the frozen‑in condition; in high‑β plasmas whistler waves dominate fast reconnection, while in low‑β plasmas kinetic Alfvén waves are key, with ion and electron motions also influenced by mass ratio and β.

Abstract

The results of kinetic simulations of magnetic reconnection in Harris current sheets are analyzed. A range of guide fields is considered to study reconnection in plasmas characterized by different β values, β>me/mi. Both an implicit particle-in-cell (PIC) simulation method and a parallel explicit PIC code are used. Simulations with mass ratios up to the physical value are performed. The simulations show that the reconnection rate decreases with the guide field and depends weakly on the mass ratio. The off-diagonal components of the electron pressure tensor break the frozen-in condition, even in low β plasmas. In high β plasmas, evidence is presented that whistler waves play a key role in the fast reconnection physics, while in low β plasmas the kinetic Alfvén waves are important. The in-plane and the out-of-plane ion and electron motion are also considered, showing that they are influenced by the mass ratio and the plasma β.