Quick initiation of magnetic reconnection in an ion scale current sheet

Masaki Fujimoto[1] ,*Iku Shinohara [2],Manfred Scholer [3]
Tokyo Institute of Technology[1]
Institute of Space and Astronautical Science[2]
Max-Planck Institute for Extraterrestrial Physics[3]

It is a very important point to understand the explosive nature of magnetic reconnection, which is still poorly understood. Many theorists believe that the turbulence in an electron-scale current sheet is necessary to provide sufficient dissipation to trigger fast reconnection in space, while there is no observational evidence that the current sheet thins down to electron scale. It is therefore an interesting question to ask if some dissipation mechanisms set in already at ion scale current sheets. In order to investigate the onset mechanism of magnetic reconnection in an ion-scale current sheet, we are carrying out a large-scale 3D PIC code simulation. The simple 1D Harris current sheet is set as the initial condition of the simulation run, and no initial perturbation, like a driven flow, is added. In such a condition, the growth of the collision less tearing mode is much slower than those of the other instabilities in the 3rd dimension (out of plane of reconnection). Contrary to our expectation, magetic reconnection occurs very quickly within about 5 ion gyro-period. Although no electric field activity is observed right at the neutral sheet, a number of wave modes are found in the boundary of the current sheet. We discuss the initiation mechanism of magnetic reconnection in connection with the observed turbulence in the boundary of the current sheet.