Plasmoid growth in 2D Full-F Gyrofluid Magnetic Reconnection

TL;DR

This paper introduces a novel Full-F gyrofluid model to simulate 2D magnetic reconnection, analyzing plasmoid growth, tearing instability, and transient amplification mechanisms relevant to fusion devices.

Contribution

It develops and applies a Full-F gyrofluid model with arbitrary wavelength polarization to study plasmoid growth and tearing instability in 2D magnetic reconnection, including non-normal transient effects.

Findings

Non-normal linear operator exhibits large transient amplification.

Plasmoid growth is influenced by aspect ratio and FLR effects.

Simulation results provide insights into explosive reconnection mechanisms.

Abstract

Plasmoid growth is considered to enhance the rate of magnetic reconnection and is frequently used to explain fast mag netic reconnection in highly conductive (collisionless) plasmas. In strongly magnetized plasmas, the long wavelength dimension parallel to the magnetic field can be separated from the small wavelength perpendicular plane, justifying an isolated 2D approach. While 2D systems have been simulated using delta F gyrofluids, a novel Full-F gyrofluid model with arbitrary wavelength polarization is used to simulate 2D Harris-sheet magnetic reconnection with domain aspect ratios Ly/Lx < 16 and investigate the corresponding plasmoid growth and tearing instability growth rates. In addition to linear tearing analysis, a non-modal stability analysis of the linearised system is performed. The evolution operator is shown to be strongly non-normal, exhibiting large condition numbers and extended pseudospectra, which indicate the possibility of significant transient amplification even in marginally stable regimes. This non-normal behavior pro vides a mechanism for explosive reconnection and helps explain the transition from linear tearing growth to rapid nonlinear acceleration. We focus on low plasma beta magnetic reconnection on the scale of the hybrid drift scale and incorporate ion finite Larmor radius (FLR) effects, putting the simulations in the perspective of magnetically confined nuclear fusion devices such as tokamaks. After discussing requirements on numerical resolution and convergence we present a parameter scan, varying the electron skin depth and the ion-to-electron temperature ratio. Finally, we present a discussion on the influence of aspect ratio, different models and possible contributions due to FLR effects.