An new MHD/kinetic model for exploring reconnection-driven particle accelerationin macroscale systems*

A novel MHD/kinetic model is being developed to explore magnetic reconnection and particle energization in macro-scale systems. The model blends the MHD description with a macro-particle description. The rationale for this model is based on the recent discovery that the most energetic particles produced during magnetic reconnection are driven by Fermi reflection rather than parallel electric fields. Since the former mechanism is not dependent on
kinetic scales such as the Debye length and the electron and ion inertial scales, a model that sheds these scales is sufficient for describing reconnection-driven particle acceleration. Our MHD/kinetic model includes macroparticles laid out on an MHD grid that are evolved with the MHD fields using the relativistic guiding center equations. Crucially, the feedback of the energetic component on the MHD fluid is included in the dynamics. Thus, energy of the total
system, the MHD fluid plus the energetic component, is conserved. The system has no kinetic scales and therefore can be implemented to model energetic particle production in macro-systems with none of the constraints associated with a PIC model. Tests of the new model in
simple geometries will be presented.