Electromagnetic particle-in-cell simulations on magnetic reconnection with adaptive mesh refinement

The electromagnetic particle-in-cell (EM-PIC) model using the adaptive mesh refinement (AMR) is reconsidered so that it is properly and efficiently applied to the current sheet evolution associated with magnetic reconnection. It is very important to adequately select the refinement criteria for cell splitting. It is demonstrated that fine cells have to be distributed not only in the region where the electron Debye length is small, but also in the region where the electron-scale structure is expected to be significant. While the AMR reduces the number of cells drastically, the total simulation cost is also controlled by the number of particles. In order to reduce the total number of particles in the entire system, the present code controls the local number of particles per cell by splitting or coalescing particles. It is shown that the particle splitting and coalescence are quite effective as well as the AMR to enhance the efficiency of the EM-PIC simulations. A new 3D code extended from the 2D code is also introduced. The code is checked against the tearing instability and the lower hybrid drift instability, and it is confirmed that the code has been successfully developed. It is also found that the 3D simulations can gain more efficiency by using the AMR than the 2D simulations.