3D Kinetic Simulations of Driven Reconnection in Merging Flux Tubes

TL;DR

This study uses 2D and 3D Particle-in-Cell simulations to explore magnetic reconnection in merging flux tubes, revealing effects of dimensionality, guide fields, and driving strength on reconnection dynamics and particle acceleration.

Contribution

It provides new insights into how 3D effects, guide fields, and external drive influence reconnection onset, rate, and particle energy spectra in pair plasmas.

Findings

3D effects delay reconnection onset compared to 2D.

Strong guide fields suppress drift-kink activity.

Particles reach a maximum energy characterized by gamma_cut/sigma_in ~ 50.

Abstract

We present 2D and 3D Particle-in-Cell simulations of driven collisionless magnetic reconnection triggered by the compression and merger of two Lundquist-type force-free flux tubes in a strongly magnetized pair plasma, with a focus on magnetic energy dissipation and particle acceleration. We show that 3D effects systematically delay the onset of reconnection in comparison with equivalent 2D runs, an effect further enhanced by a strong guide field, due to reduced linear growth rates and phase decoherence of oblique modes. Increasing the external drive accelerates both tearing and drift-kink instabilities, while a strong guide field suppresses coherent drift-kink activity and has a comparatively mild impact on tearing. Despite these differences in early-time dynamics, all simulations enter a fast-merging phase characterized by a normalized reconnection rate 0.08--0.10, coinciding with a transient reduction of the guide-to-reconnecting field ratio inside the current sheet. The high-energy cutoff of accelerated particles converges to a common asymptotic value, gamma_cut/sigma_in ~ 50, with only a weak dependence on the driving strength. This behavior is consistent with an electric-field-limited acceleration process, in which the maximum energy is set by the reconnection electric field and the duration of the energization phase. The resulting nonthermal particle spectra are similar across all runs, with power-law indices p ~ 1.6--2.0.