CAREER: Magnetogenesis Revisited: The First Self-consistent Plasma Dynamo

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

The universe is magnetized. From galaxies and galaxy clusters to the solar system, including the Sun and our own planet, magnetic fields are found nearly everywhere we look. Their ubiquitous presence is not passive; rather, magnetic fields are key players in the dynamics and shape of the observable universe. Such phenomena can have significant societal implications here on Earth, as illustrated by the case of solar flares. Solar flares are dramatic manifestations of magnetic activity in the Sun that impact directly space weather and may catastrophically affect the national electric power grid. Therefore understanding the mechanisms responsible for cosmic magnetic fields is an important challenge in plasma physics. This landscape provides a fertile area of research and training for students. This project will lead to the development of novel analytical theoretical methods and state-of-the-art supercomputer simulations. This project will focus on reassessing the importance of the initial magnetic fields that are required to seed any dynamo. In the usual paradigm, the conventional assumption is that these arise via the Biermann battery. Such fields are system-size and weak. In collisionless plasmas, however, recent ab initio results suggest that an altogether different paradigm may be more appropriate; indeed, numerical simulations show that the configuration that gives rise to the Biermann fields becomes prey to the electron Weibel instability. The seed fields that ensue are radically different from those of Biermann origin: they are fairly strong, and live at scales close to the electron skin-depth. This result thus points to a different scenario: the plasma dynamo problem may not, in fact, be as much about amplitude as it is about scale: can electron-scale fields, under the combined action of their own nonlinear evolution and background turbulence, give rise to a large scale field at equipartition levels? Assessing how such seed fields evolve and, critically, whether a plasma dynamo seeded in this fashion may indeed exist, is the key goal in this project.