Experimental Verification of the Hall Effect during Magnetic Reconnection in a Laboratory Plasma

In this Letter we report a clear and unambiguous observation of the out-of-plane quadrupole magnetic field suggested by numerical simulations in the reconnecting current sheet in the magnetic reconnection experiment. Measurements show that the Hall effect is large in the collision-less regime and becomes small as the collisionality increases, indicating that the Hall effect plays an important role in collision-less reconnection.