Do plasmoids induce fast magnetic reconnection in well-resolved current sheets in 2D MHD simulations?

Do plasmoids induce fast magnetic reconnection in well-resolved current sheets in 2D MHD simulations?
G. H. Vicentin, G. Kowal, E. M. de Gouveia Dal Pino, A. Lazarian
arXiv:2510.01060v5 Announce Type: replace-cross
Abstract: We investigate the development of tearing-mode instability using the highest-resolution two-dimensional magnetohydrodynamic simulations of reconnecting current sheets performed on a uniform grid, for Lundquist numbers of $10^3 le S le 5 times 10^5$ , reaching up to $65,536^2$ grid cells. We demonstrate a Sweet–Parker scaling of the reconnection rate $V_{text{rec}} sim S^{-1/2}$ up to Lundquist numbers $S sim 10^4$. For larger values of Lundquist number, between $2times 10^4le S le 2 times 10^5$, plasmoid formation sets in, leading to a slight enhancement of the reconnection rate, $V_{text{rec}} sim S^{-1/3}$, consistent with the prediction from linear tearing mode induced reconnection, indicating that reconnection remains resistivity-dependent and therefore slow. In this range of $S$-values, the plasmoids do not undergo a merger cascade, as they are rapidly advected out of the reconnection layer. Only for $S > 2 times 10^5$, we observe the nonlinear development of the tearing-mode instability, with plasmoid coalescence and a saturation of the reconnection rate at $V_text{rec} / V_A sim 0.01$. At such high $S$, however, the corresponding Reynolds number is large, reaching $text{Re} > 2000$ even on scales comparable to the current-sheet thickness. We therefore conclude that, in astrophysical systems, it is essential to account for the dominant influence of turbulence and three-dimensional effects in the reconnection process.arXiv:2510.01060v5 Announce Type: replace-cross
Abstract: We investigate the development of tearing-mode instability using the highest-resolution two-dimensional magnetohydrodynamic simulations of reconnecting current sheets performed on a uniform grid, for Lundquist numbers of $10^3 le S le 5 times 10^5$ , reaching up to $65,536^2$ grid cells. We demonstrate a Sweet–Parker scaling of the reconnection rate $V_{text{rec}} sim S^{-1/2}$ up to Lundquist numbers $S sim 10^4$. For larger values of Lundquist number, between $2times 10^4le S le 2 times 10^5$, plasmoid formation sets in, leading to a slight enhancement of the reconnection rate, $V_{text{rec}} sim S^{-1/3}$, consistent with the prediction from linear tearing mode induced reconnection, indicating that reconnection remains resistivity-dependent and therefore slow. In this range of $S$-values, the plasmoids do not undergo a merger cascade, as they are rapidly advected out of the reconnection layer. Only for $S > 2 times 10^5$, we observe the nonlinear development of the tearing-mode instability, with plasmoid coalescence and a saturation of the reconnection rate at $V_text{rec} / V_A sim 0.01$. At such high $S$, however, the corresponding Reynolds number is large, reaching $text{Re} > 2000$ even on scales comparable to the current-sheet thickness. We therefore conclude that, in astrophysical systems, it is essential to account for the dominant influence of turbulence and three-dimensional effects in the reconnection process.