On Modeling the Interaction between Fluid and Kinetic Scales

Brackbill Jeremiah U, Portland OR

Investigators

Abstract

Magnetofluid (MHD) calculations model large scales and long times, but eliminate kinetic effects. In the landscape in between, there are reduced models such as hybrid and gyrokinetic models, and there are implicit methods, which extend plasma simulations to larger scales while retaining the contributions of kinetic electrons. An increase in applicability of any of these methods would be useful. Here the PI proposes to extend implicit methods to problems on MHD timescales. It is proposed first to implement the Hall-MHD limit of the implicit moment equations, and to verify that it will give correct results for standard problems,such as the GEM reconnection challenge. Second, interface conditions between kinetic and Hall-MHD regions will be developed. These require continuity in the field solutions, flux matching conditions for the fluid moments, and consistent boundary conditions for kinetic particles. These will be tested for uniform flows, and for a resolved kinetic calculation of the lower hybrid drift instability enclosed within a stretched Hall-MHD grid. Third, current sheets threaded by open field lines will be modeled in two and three dimensions with special attention to the sensitivity to MHD domain outer boundary conditions, and the role of parallel currents. This activity will advance discovery, both by introducing a new and improved method to the community and by applying that method to initial problems of great relevance to the larger problem of magnetic reconnection. This award is primarily to enable broad dissemination the the research. In the long run, an understanding of this physics, which concerns the earth-space-sun system, will benefit society because that system affects radio communications, space travel, and other human enterprises. Finally, the multi-scale simulation capabilities to be developed by the proposed work and related efforts are potentially transformative of the field, and of related fields.