Energetics of Kinetic Reconnection in a Three-Dimensional Null-Point Cluster

We perform three-dimensional particle-in-cell simulations of magnetic reconnection with multiple magnetic null points. Magnetic field energy conversion into kinetic energy is about five times higher than in traditional Harris sheet configuration. More than 85% of initial magnetic field energy is transferred to particle energy during 25 reversed ion cyclofrequencies. Magnetic reconnection in the cluster of null points evolves in three phases. During the first phase, ion beams are excited, then give part of their energy back to the magnetic field in the second phase. In the third phase, magnetic reconnection occurs in many small patches around the current channels formed along the stripes of a low magnetic field. Magnetic reconnection in null points essentially presents three-dimensional features, with no two-dimensional symmetries or current sheets.

Figure 1

(a), (b), (c) Snapshots of a magnetic field at different times (labelled in the upper left). Field lines are plotted in different colors; each color corresponds to the lines passing by one of 8 initial null points. Isocontours of low magnetic field $B=0.1B_0$ are plotted in grey. (d) Snapshot of current $J$ made at ${\Omega }_{ci}t=1.6$.

Figure 2

Evolution of different components of energy (total kinetic energy of particles, magnetic field energy, bulk and thermal energy of both species).

Figure 3

Snapshots of the electron-frame dissipation measure $D_e$ (upper panels) and parallel electric field $E_{\parallel }$ (lower panels) in the lower half of the computational domain spanning from $Z=0$ to $Z=5d_i$ at different times (labelled in the upper left of each column). Isocontours of low magnetic field $B=0.1B_0$ are plotted in grey.