Direct evidence of secondary reconnection inside filamentary currents of magnetic flux ropes in magnetic reconnection

Magnetic reconnection is a fundamental plasma process, by which magnetic energy is explosively released in the current sheet to energize charged particles and to create bi-directional Alfvénic plasma jets. A long-outstanding issue is how the stored magnetic energy is rapidly released in the process. Numerical simulations and observations show that formation and interaction of magnetic flux ropes dominate the evolution of the reconnecting current sheet. Accordingly, most volume of the reconnecting current sheet is occupied by the flux ropes and energy dissipation primarily occurs along their edges via the flux rope coalescence. Here, for the first time, we present in-situ evidence of magnetic reconnection inside the filamentary currents which was driven possibly by electron vortices inside the flux ropes. Our results reveal an important new way for energy dissipation in magnetic reconnection.