Numerical study and modeling on the feedthrough mechanism of double-interface Rayleigh–Taylor instability growth

Multi-interface Rayleigh–Taylor (RT) instability is one of the critical factors limiting the performance of double-shell inertial confinement fusion (ICF) targets. This work presents a study on double-interface RT instability. The right interface is subject to RT instability, while the left interface is mainly driven by feedthrough. At the right interface, spike growth remains decoupled from the left interface. In contrast, bubble growth is strongly suppressed by feedback from the left side, especially for thinner shells. This result differs from the vacuum-bounded limit of Baker et al. [J. Fluid Mech. 178, 161 (1987)], which stems from the absence of drag in vacuum vs the strong drag present in our finite-density configuration. At the left interface, bubble growth converges to the evolution pattern of the right side, while the spike region exhibits concurrent in-phase growth and anti-spike formation. The anti-spike forms when the restoring effect locally overwhelms the feedthrough-driven growth. We then quantify the roles of shell thickness, wavelength, Atwood number, and acceleration. Bubble feedthrough increases with thinner shells and larger values of the other parameters. In contrast, effective spike feedthrough shifts negatively when the shell thickness and left Atwood number increase, but positively when the other parameters increase. Based on these insights, we extend the classical buoyancy-drag model by modeling the shell-thinning processes and effects, and introducing the transition mechanism between the thin-shell and thick-shell regimes. The extended model retains the accuracy of the original formulation under common conditions, while delivering clearly improved predictions when the drag becomes significant.