Electron energization during magnetic island coalescence

Radio emission from colliding coronal mass ejection flux ropes in the interplanetary medium suggested the local generation of superthermal electrons. Inspired by those observations, a fully kinetic particle-in-cell simulation of magnetic island coalescence models the magnetic reconnection between islands as a source of energetic electrons. When the islands merge, stored magnetic energy is converted into electron kinetic energy. The simulation demonstrates that a mechanism for electron energization originally applied to open field line reconnection geometries also operates near the reconnection site of merging magnetic islands. The electron heating is highly anisotropic, and it results mainly from an electric field surrounding the reconnection site that accelerates electrons parallel to the magnetic field. A detailed theory predicts the maximum electron energies and how they depend on the plasma parameters. In addition, the global motion of the magnetic islands launches low-frequency waves in the surrounding plasma, which induce large-amplitude, anisotropic fluctuations in the electron temperature.