Gyrofluid Magnetic Reconnection Beyond the δ F Approximation

Abstract

Magnetic reconnection in a two-dimensional system is studied employing a novel Full-F gyrofluid model with arbitrary- wavelength polarization. In strongly magnetized plasmas, the long wavelength dimension parallel to the magnetic field can be separated from the much smaller perpendicular scales, motivating an isolated two-dimensional description. While previous studies have predominantly employed delta- F gyrofluid models, the present Full-F formulation is applied to simulate Harris-sheet magnetic reconnection with domain aspect ratios L_y/L_x <= 16, investigating tearing-mode growth, plasmoid formation, and the influence of finite ion Larmor radius (FLR) effects. In addition to a linear tearing-mode analysis, a non-modal stability analysis of the linearized system is performed. The evolution operator is shown to be strongly non-normal, exhibiting large condition numbers and extended pseudospectra that indicate the possibility of significant transient amplification, even in marginally stable regimes. Such transient amplification may facilitate the transition from linear tearing growth to rapid nonlinear acceleration. We focus on low-plasma-beta magnetic reconnection on the scale of the drift scale and incorporate ion FLR effects, placing the simulations in the context of magneti- cally confined fusion plasmas such as tokamaks. After discussing numerical resolution and convergence, we present a parameter scan varying the normalized electron skin depth and the ion-to-electron temperature ratio. Finally, the influence of aspect ratio, polarization model, and FLR effects on the reconnection dynamics and plasmoid formation is investigated.