Topological Bifurcation Triggers Magnetic Reconnection in a Mini-Magnetopause

Magnetic reconnection is a fundamental plasma process responsible for the rapid conversion of magnetic energy into plasma particle energy. This process is observed in a wide range of astrophysical, space, and laboratory environments such as solar flares, Earth's magnetic storms, and disruptions in fusion devices. Despite its critical role in explosive phenomena, the trigger mechanism for transitioning from a stable or quasi-stable 3D magnetic configuration to a field configuration with fast energy conversion remains a significant unresolved issue. In this laboratory experiment, a topological bifurcation initiated the onset of fast magnetic reconnection in a mini-magnetopause. Driven by the rapidly changing angle of the background magnetic field, separatrix surfaces were forced to intersect. The crossing of these separatrixes birthed magnetic null points and reshaped the separator line, constituting a bifurcation in the magnetic topology. Simultaneously, the reconnection electric field increased significantly. This observation, that a geometric reconfiguration of a 3D magnetic topology can trigger reconnection, may have broad implications across plasma regimes. If introduced into predictive models, it has the potential to improve the understanding of space weather, astrophysical explosions, and plasma confinement systems.