UCLA

Many planetary bodies can generate and sustain large-scale magnetic fields. The kinetic energy of electrically conducting fluids inside the bodies converts into magnetic energy through so-called "dynamo" processes. Turbulent thermo-chemical convective flows in a planet’s electrically conducting fluid core often generate a planetary-scale, dipole-dominated magnetic field. The magnetic field generated by dynamo processes acts back on the convective flow via Lorentz forces, creating a complex turbulent magnetohydrodynamic (MHD) system. Investigating the planetary dynamos will elucidate the fundamental dynamics of planetary interiors, providing essential information on the formation and evolution of the host planet. Moreover, strong planetary-scale magnetic fields can shield the planets from high-energy cosmic radiation and charged particles from the stars, making dynamo study crucial for habitability and searching for life on candidate bodies in the solar system and other exoplanetary systems.

In this thesis, I present a series of laboratory experiments to investigate the essential force balance and turbulence dynamics of planetary-core-style convection, in which magnetic field, rotation, and thermal buoyancy are applied to a liquid metal (gallium) fluid body on the RoMag device. These experimental investigations help bridge dynamics at planetary core boundaries and the interior of the fluid core, providing valuable insights into the fundamental physics of dynamo processes. They also provided an experimental pathway to connect small-scale dynamics that can be studied in the laboratory and large-scale dynamics within the planetary cores. This pathway is essential as current numerical simulations and experiments cannot capture large-scale dynamics directly.

I investigate the MHD effects at the planetary boundaries using a simplified end-member system of core-style convection: non-rotating magnetoconvection (MC). I have characterized a self-sustaining thermoelectric effect in liquid metal turbulent MC with electrically conducting boundaries. The thermoelectric currents at the boundaries generate a large-scale precession of the turbulent convective flow. To explain this phenomenon, I have developed a solid-liquid analytical model that predicts precession frequencies agreeing with the lab data. This model also produces a set of new dimensionless parameters to describe under what conditions the thermoelectric effect could become prominent near the Earth's core-mantle boundary (CMB).

Furthermore, I study liquid metal MC's heat transfer and behavior regimes from onset to highly supercritical. I have compared the effects of magnetic constraints in MC with the rotational constraints. With a better understanding of the MC system as a building block, I have carried out a set of rotating convection (RC) and rotating magnetoconvection (RMC) experiments to probe the internal flow dynamics of planetary cores. Our preliminary results hint that the turbulent liquid metal RC can form large-scale, barotropic vortices through an inverse cascade in kinetic energy. This stairway of energy cascade could potentially connect laboratory scale dynamics to planetary scale flows and provide insights into the dynamical origin of the observed large-scale magnetic structures.