This project will develope a new code for the simulation of magnetic reconnection. The code will treat the electrons and ions as separate but coupled fluids. The first step will be the development of a solver for the equations of the electric field and magnetic field. The next step is to develop a module that solves for the equations governing the electron fluid. This module will have the capability of switching on or off different terms in the electron equations in order to study the effects of the different terms. Once the electron fluid code has been fully developed the ion fluid modlue can be quickly derived from the electron fluid. The final step will be to couple the electron and ion fluids and the electric and magnetic field solvers.
By treating the electrons and ions as separate fluids the new code will have the ability to investigate cross-scale coupling in collisionless magnetic reconnection. Collisionless reconnection is the most important process that couples the energy in the solar wind into Earth's magnetosphere and eventually down to the ionosphere and neutral atmosphere. Collisionless reconnection is also a critically important process in the generation of magnetic substorms and storms.
Magnetic reconnection is a fundamental processes in nature for converting magnetic energy to kinetic energy. The magnetic field structure changes drastically during reconnection and a hallmark of the transformation is the emergence of a quadrupole structure. The processes at the shortest scale correspond to the dynamics of the elctrons and these were simulated using a numerical codes based on the electron-magnetohydrodynamics (EMHD) model and showed a nested structure of the quadrupole magnetic field. These and other results obtained from the EMHD model provide the shortest scale features of collisionless reconnection. However these results obtained from the simplified model of electron dynamics can be affected by the processes in which the ions, whch are about 2000 times heavier, play a significant role. The main objective of the project was to study the effect of the ions on the electron scale processes and the cross-scale coupling. This requires the development of a two-fluid code so that the dynamics of both the electrons and ions are included in the simulation. Such a code uses the equations describing the electron and ions and their coupling through Maxwell euation, which are integrated numerically taking care the electron processes are well resolved and in the same time the ions effects are considered in the time evolution. This is a challenging problem due the complicated nature of the equations and the need to cover the widely separated electron and ion dynamics simultaneouly. In this project two forms of these equations were considered and their performances evaluated. The two-fluid simulations show the nested quadrupole structure of the magnetic filed during collisionless reconnection, thus verifying the results of the EMHD simulations. These results provided details directly relevant to the multispacecraft NASA/MMS mission, which is the first mission designed to explore the spatial and temporal features of electron scale processes in the Earth's magnetosphere. The intellectual merit of the project is the understanding of the shortest scale processes in magnetic reconnection using the simple model (EMHD) and the more sphisticated two-fluid simulations developed in the project. In particular the nested structure of the quadrupole magnetic field at the electron scale is shown to be a basic feature of reconnection. The broader impacts of the project are mainly from the development of the two-fluid numerical code, which is a significantly big effort and has direct applications to other areas such as fluid dynamical simulations. The science results are directly relevant to the broader areas of explorations of the fundamental processes in reconnection using spacecraft missions, e. g., NASA/MMS mission, and laboratory experiments. One post-doctoral fellow and one graduate student participated in the project, in the research in plasma physics and in the development of numerical codes. The experience of these participants contribute directly to the training of future manpower in the areas of plasma physics, computer simulation and research using data from spacecraft and laboratory experiments.
