Magnetic reconnection and turbulence are the two most important energy dissipation processes in plasma. These two processes intertwine with each other and play important roles in their respective dynamic evolution. Here, we present the first evidence that secondary reconnections occur in the turbulent outflow driven by a primary reconnection in the Earth's magnetotail. We have identified 14 secondary reconnections in a large number of current filaments in the turbulent outflow, which persisted for about one and half an hour. Most of these secondary reconnections were electron‐only reconnection that has recently been discovered in the magnetosheath. These secondary reconnections entangled the magnetic field lines and dissipated the magnetic energy in the outflow region far away from the primary X line.

Magnetic reconnection efficiently converts magnetic energy into kinetic and thermal energy of plasmas. The electric field at the X-line, which represents the reconnection rate, is commonly used to measure how fast the reconnection proceeds. However, the energy conversion rate (ECR) has rarely been investigated. Using a 2.5D particle-in-cell simulation, we have examined the temporal evolution of the ECR in collisionless reconnection. It is found that the ECR reaches peak significantly later than the reconnection rate does. This is because the energy conversion primarily occurs at the reconnection fronts rather than at the X-line. With the increase of the inflow density, both the reconnection rate and the conversion rate decrease. The presence of a guide field leads to the reduction of both the reconnection rate and the conversion rate, though reconnection remains fast. We further find that ECR does not depend on the mass ratio but is sensitive to the length of the simulation domain.

We have performed a particle-in-cell simulation to understand the dynamic evolution of the dipolarization front during its early stage after ejected by magnetic reconnection, focusing on the force and energy balance around the dipolarization front. We track the temporal evolution of the force and different energy channels in the Lagrangian frame of the dipolarization front. We find that the curvature force continuously accelerates the dipolarization front moving outward, while the thermal pressure gradient force hinders the movement of the DF. The DF is accelerated outward because the total force is positive. The maximum value of B z at the DF gradually increases during the outward propagation of the front. Although the dipolarization front is the site with significant energy conversion from the magnetic field to plasma, that is, J • E > 0, the compression of the magnetic field by the convergent flow at the front leads to the gradual enhancement of B z. The released magnetic energy bulk accelerates and heats the plasma. The plasma thermal energy increases at the front that is primarily due to the work of the pressure gradient (v • (∇ • P) > 0), while the enthalpy flux emitted from the front reduces the thermal energy. Both the pressure-strain interaction −(P′ • ∇) • v and the pressure dilation p∇ • v contribute to the ion and electron temperature enhancement. Our results are important for revealing the dynamic evolution of the dipolarization fronts and will aid us to understand the energy transport in the disturbed magnetotail. Plain Language Summary Dipolarization front is a common structure in Earth's magnetotail. As a derivant of magnetic reconnection, the dipolarization front is generated at the X-line and propagates earthward. Scientists believe that dipolarization fronts play important roles in the energetics of the magnetotail; however, many details of this process are missing. Using particle simulation, we are able to study the force and energy balance around the dipolarization front in detail. We find that it is the curvature force that accelerates the dipolarization front moving away from the reconnection site. At the dipolarization front, different energy channels exchange. Poynting flux feeds the magnetic energy, which is dissipated to heat plasma around the front. The energy exchange and transport at the dipolarization front will shed new light on understanding the energy cycle in our magnetosphere.