Numerical simulation of compositional distribution induced by isotopologue fractionation during solidification of D–T fuel in inertial confinement fusion targets

In inertial confinement fusion, the homogeneity of deuterium (D)–tritium (T) fuel is critical to target performance. However, during solidification, isotopologue fractionation can induce non-uniform distribution of composition in the solid D–T layer and alter the equilibrium composition of the central D–T gas. This study quantifies the impact of isotopologue fractionation on the compositional distribution within a cryogenic D–T target. A comprehensive numerical framework integrating heat transfer, species transport, solidification, and volumetric shrinkage was established using ANSYS Fluent to simulate the evolution of compositional distribution during the layering process. The results show that the solid layer develops a radial mole fraction gradient; the D-atom content in the central gas becomes significantly excessive. This effect is amplified when the inner-to-outer radius ratio of the solid layer decreases and when isotopic exchange in the D–T fuel is incomplete. Such fuel inhomogeneity adversely affects fusion performance across multiple stages. The simulation approach presented here provides a quantitative tool for evaluating isotopologue fractionation in cryogenic D–T targets and offers theoretical guidance for the design and fabrication of high-performance, homogeneous targets.