Intermittent energy dissipation by turbulent reconnection
Résumé
Magnetic reconnection−-the process responsible for many explosive phenomena in both nature and the laboratory−-is efficient at dissipating magnetic energy into particle energy. To date, exactly how this dissipation happens remains unclear, owing to the scarcity of multi-point measurements of the 'diffusion region' at the sub-ion scale. Here we report such a measurement by Cluster−-four spacecraft with separation of 1/5 ion scale. We discover numerous current filaments and magnetic nulls inside the diffusion region of magnetic reconnection, with the strongest currents appearing at spiral nulls (O-lines) and the separatrices. Inside each current filament, kinetic-scale turbulence is significantly increased, and the energy dissipation, E'*J, is 100 times larger than the typical value. At the jet reversal point, where radial nulls (X-lines) are detected, the current, turbulence, and energy dissipations are surprisingly small. All these features clearly demonstrate that energy dissipation in magnetic reconnection occurs at O-lines but not X-lines.