Formulating a theoretical scaling for dispersion in MHD turbulence

One of the most fundamental aspects of turbulent flows is dispersion – a measure of how particles spread out. In electrically neutral fluids such as air and water, dispersion determines how moisture, particulates, or chemicals mix into the atmosphere or oceans. Other fluids, like liquid metals and plasmas, can carry an electrical charge.

Their movement is fundamentally changed by the presence of magnetic fields and is described by magnetohydrodynamics. Dispersion in magnetohydrodynamic fluids determines the properties of space weather as plasma spreads in the interstellar medium, how chemicals from the core of a star are mixed into its outer layers, and how particles are trapped in the liquid metal blankets of reactors.

The goal of this project is to provide a clear understanding of how magnetohydrodynamic dispersion differs from dispersion in the hydrodynamic case observed in air or water. This project will include summer research students, a computational physics outreach program using scientific visualizations and computer renderings, and technical training for the scientific/industrial work force.

This project will leverage modern ideas and theoretical techniques to modify and extend the theory of dispersion, developed by Richardson in 1926 for hydrodynamic fluids, to the setting of magnetohydrodynamic fluids. Testing our new prediction will require simulations that are particularly intensive; these simulations will be performed on some of the largest supercomputers in the world.

The simulation data will allow our theoretical results to probe questions of foundational importance for magnetohydrodynamic turbulence. These include how a turbulent flow develops a preferred direction of movement, and how different parts of the flow interact energetically. The results of our theoretical and computational investigation will allow engineers to design more efficient reactors, and astronomers to better predict the space weather that impacts life on Earth.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.