Formation and Interaction of Magnetic Flux Ropes in Kinetic-Scale Current Layers

In space plasmas, current sheets arise spontaneously from the interaction of flows or magnetic structures. As these current layers approach kinetic scales, they may become unstable to the collisionless tearing instability, resulting in the formation and interaction of magnetic flux ropes. While theoretical treatments of the tearing instability have largely focused on 1D equilibria with periodic boundary conditions, current sheets in nature have a finite spatial extent and are embedded within a larger open system. In many applications, the field boundary conditions are line-tied as in the case of flux ropes on the dayside magnetopause where the ionosphere acts as a conducting surface. To assess the applicability of existing linear tearing theory to these more realistic configurations, we consider a series of 3D kinetic simulations of force-free current layers with line-tied boundary conditions for the fields and open boundaries for the particles. The geometry and plasma parameters are motivated by a new laboratory experiment on the Large Plasma Device at UCLA. For sufficiently long systems, we demonstrate that key aspects of the theory remain valid. New diagnostics are employed to characterize the nonlinear reconnection rate and the structure of the magnetic field.