Fast Cross‐Scale Energy Transfer During Turbulent Magnetic Reconnection

Magnetic reconnection is a key fundamental process in collisionless plasmas that explosively converts magnetic energy to plasma kinetic and thermal energies through a change of magnetic field topology in a central electron‐scale region called the electron diffusion region (EDR). Past simulations and observations demonstrated that this process causes efficient energy conversion through the formation of multiple macro‐scale or micro‐scale magnetic islands/flux ropes. However, the coupling of these phenomena on different spatiotemporal scales is still poorly understood. Here, based on a new large‐scale fully kinetic simulation with a realistic, initially fluctuating magnetic field, we demonstrate that macro‐scale evolution of turbulent reconnection involving merging of macro‐scale islands induces repeated, quick formation of new electron‐scale islands within the EDR which soon grow to larger scales. This process causes an efficient cross‐scale energy transfer from electron‐ to larger‐scales, and leads to strong electron energization within the growing islands. Plain Language Summary Space above the Earth’s atmosphere is broadly filled with ionized gas, called plasma. Since the density of the space plasma is mostly small enough to neglect the viscosity, the behavior of it is essentially different from neutral viscous fluids. In such a collisionless plasma system, the boundary layer between regions with different electromagnetic field and plasma properties plays a central role in transferring energy. One of the representative energy transfer processes in collisionless plasmas is magnetic reconnection that explosively converts magnetic energy to plasma kinetic energy through the topology change of magnetic field lines across the boundary layer with a large magnetic shear. On the other hand, understanding how the energy transfer between different spatiotemporal scales in turbulence, which has been commonly observed in space, is also a key for understanding the energy transfer physics in collisionless plasmas. In this study, based on a new plasma kinetic simulation of magnetic reconnection newly considering realistic, turbulent magnetic field fluctuations, it is found that during macro‐scale evolution of the background fluctuations, the topology change of the reconnecting field lines occurs at multiple points within the micro‐scale central region of reconnection. This process causes an efficient cross‐scale energy transfer from micro‐ to larger‐scales. Key Points