Future fusion reactors may employ flowing liquid metals, such as lithium, to protect plasma-facing walls. These liquid films can absorb extreme heat loads, reduce material erosion, and improve plasma confinement. Yet their success depends critically on whether the films remain smooth and stable under the combined action of gravity, surface tension, and powerful magnetic fields inside a reactor. If the surface ruptures or drips, it can expose the underlying solid wall and contaminate the plasma with metal—undermining reactor performance.

In this project, we developed theoretical models and numerical simulations to analyze the Rayleigh–Taylor instability of thin conductive films in strong magnetic fields. Classical theory shows that a heavier fluid sitting atop a lighter one is unstable, but our work extended this picture to finite-thickness, electrically conductive films relevant for liquid lithium in tokamaks. We demonstrated that horizontal magnetic fields strongly suppress instability growth, especially for long-wavelength disturbances, and that surface tension further narrows the unstable window of modes. Using customized magnetohydrodynamic solvers, we confirmed these predictions and mapped out the regimes where lithium films can remain intact on reactor walls.

By identifying the stability limits of liquid-metal coatings, this work provided essential design rules for plasma-facing components in future reactors. It showed that carefully chosen magnetic configurations and film thicknesses can stabilize lithium films against disruptive instabilities, helping to unlock the promise of liquid-metal walls for sustainable fusion energy.

Publications

  • 📄 F. Yang, A. Khodak, and H. A. Stone. The effects of a horizontal magnetic field on the Rayleigh-Taylor instability. Nuclear Materials and Energy (2019). HTML
  • 📄 A. Khodak, F. Yang, and H. A. Stone. Free-Surface Liquid Lithium Flow Modeling and Stability Analysis for Fusion Applications. Journal of Fusion Energy (2020). HTML

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