Modeling fusion target interfaces across large length scales and timescales poses significant challenges when stochastic fluctuations and heterogeneous dynamics are involved. Traditional approaches use precomputed interaction potentials based on bulk thermodynamic properties; however, fusion targets involve extreme spatiotemporal variations in temperature, density, and charge distributions that violate these assumptions. In particular, at heated interfaces between plastic ablators and deuterium-tritium fuel layers, heterogeneous charge separation and ion transport exhibit electrochemical-like behavior that cannot be captured by conventional mean-field descriptions. Here, we present a multiscale stochastic approach to orbital-free density functional theory molecular dynamics (OFDFT-MD) simulations that bridges atomic, ionic, and continuum scales while explicitly incorporating fluctuations and randomness. Our approach enables simulations on micron length scales and 10's of picosecond timescales, exceeding current capabilities by orders of magnitude.
This new capability is used to study the heterogeneous, nonequilibrium dynamics of inertial-confinement-fusion capsule interfaces. At these scales, we observe features such as stochastic charge separation, correlated ion transport pathways, and hydrogen jetting dynamics that had previously not been captured in deterministic hydrodynamic simulations. This work demonstrates how stochastic modeling approaches from electrochemical systems can provide new insights into fusion target interface physics and inform interaction kernel development for multi-scale fusion simulations.
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