Large-Scale Self Organization in Three-Dimensional Shear-Flow-Driven Magnetized Plasma Turbulence

In the universe, smooth magnetic fields are observed in very large systems like galaxies and can be generated by electrically conducting flowing matter, such as a plasma. Plasma flows that change direction from one region to another are said to be unstable and spontaneously generate turbulence, which creates magnetic fields that are tangled instead of smooth. In this project, computer simulations will be used to explore how magnetic fields are created in turbulent plasma systems and how these magnetic fields become smooth. Examples of such systems include the generation of zonal flows observed in fusion plasma devices and are analogous to the bands that are seen in the atmosphere of Jupiter. This project will also examine how the large magnetic field structures that are seen in these flows break up and re-form to understand when and why this happens. This award supports a study of the formation of large-scale anisotropic structures in three-dimensional (3D) magnetized plasma turbulence driven by a maintained unstable shear flow. The project builds on prior studies of two-dimensional (2D) magnetized plasma turbulence showing the sequestering of magnetic energy at large scales due to the excitation of a stable mode conjugate to the Kelvin-Helmholtz unstable mode. It also builds on analyses of 3D hydrodynamic turbulence, which have showed the generation of a zonal flow via a process involving the interaction of 2D unstable modes, weakly driven 3D unstable modes, and a conjugate stable mode. A versatile numerical modeling code Dedalus will be used for the project, employing newly developed diagnostics to track spectral energy transfer within the system. The project also includes a collaboration with the Dutch Institute for Fundamental Energy Research within the Eindhoven University of Technology in the Netherlands. 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.