Reconnection Rate in Collisionless Magnetic Reconnection under Open Boundary Conditions

Collisionless magnetic reconnection is studied by using two-dimensional
Darwin particle-in-cell simulations with different types of open boundary conditions. The simulation results indicate that reconnection rates are strongly dependent on the imposed boundary conditions of the magnetic field B_x in the inward side. Under the zero-gradient B_x boundary condition, the reconnection rate quickly decreases after reaching its maximum and no steady-state is found. Under both electromagnetic and magnetosonic boundary conditions, the system can reach a quasi-steady state. However, the reconnection rate E_r≈0.08 under the electromagnetic boundary condition
is weaker than E_r≈0.13 under the magnetosonic boundary condition.