Identification of Y-shaped and O-shaped diffusion regions during magnetic reconnection in a laboratory plasma

摘要

Two strikingly different shapes of diffusion regions are identified during magnetic reconnection in a magnetohydrodynamic laboratory plasma. The shapes depend on the third vector component of the reconnecting magnetic fields. Without the third component (anti-parallel or null-helicity reconnection), a thin double-Y shaped diffusion region is identified. In this case, the neutral sheet current profile is accurately measured to be as narrow as the order of the ion gyro-radius. In the presence of an appreciable third component (co- helicity reconnection), an O-shaped diffusion region appears and grows into a spheromak configuration.