Simulations Of 2-D MHD Turbulent Reconnection Under Different Lundquist Numbers

Magnetic reconnection is a fundamental plasma phenomenon that occurs in a wide range of applications in laboratory,space and astrophysical plasma,including earth and planetary magnetosphere,solar flare,solar wind,nuclear fusion device and high energy density explosion.Magnetohydrodynamics(MHD)theory is a classical theory commonly used to describe magnetic reconnection.Magnetic reconnection in space plasma often occurs in highly turbulent environments.Therefore,it is particularly important to understand the properties of magnetic reconnection in these turbulent environment.Taking turbulence into account in MHD model by numerical simulation thus becomes a crucial topic.In this work,we use high-resolution two-dimensional(2D)MHD simulations with different Lundquist numbers to study the physical mechanism of turbulent reconnection and the role of turbulence in enhancing the reconnection rate.In the simulation,turbulence is injected into the system from the outside with different intensities.We found that turbulence could enhance the reconnection rate via at least two mechanisms.Frist,the externally driven turbulence itself helps the system to convert the magnetic energy into the plasma kinetic energy expelled from the downstream area of reconnection,so as to improve the reconnection rate.Second,the plasma magnetic island formed at high Lundquist number is also helpful to accelerate reconnection.In addition,the existence of turbulence has a great influence on magnetic energy conversion.When the turbulence intensity is small,the magnetic field energy is mainly converted into plasma kinetic energy via Ohmic dissipation.When the turbulence intensity is high,the magnetic field energy is mainly converted into plasma kinetic energy by non-Ohmic dissipation.At the same time,turbulence has an impact on the Kelvin-Helmholtz instability in the process of magnetic reconnection.A strong turbulence facilitates the formation of a configuration in the downstream region of the magnetic field,which is favorable for the development of Kelvin-Helmholtz instability.Finally,we discuss the properties of turbulence in turbulent reconnection.We find that there are obvious differences between twodimensional turbulence and three-dimensional turbulence.This difference is mainly reflected in the power relationship between parallel and perpendicular energy spectra.