Effect of capsule thickness on the nonlinear hydrodynamic evolution of isolated surface defects

Abstract Isolated surface defects, ranging from submicron to tens of microns, are believed to degrade implosion performance in inertial confinement fusion targets. A systematic study of localized perturbation growth, determined by defect size and capsule thickness, is conducted using a simplified planar model. When the defects appear as pits and the capsule thickness is relatively small, distinct features such as bubble expansion and spike closure, which are characteristic of isolated defects and were recently reported by Zulick et al (2020 Phys. Rev. Lett. 125 055001), can be observed. In contrast, thicker capsules exhibit phase inversion and multimode behavior in the dominant modes of both pit and bump defects, due to perturbation wave propagation. Consequently, Rayleigh–Taylor (RT) instability seeds at the acceleration phase differ significantly between thin and thick capsules, even with identical defects. Capsules of the same thickness produce similar RT perturbation spectra, even with different defect types. An artificial neural network (ANN) model capable of quantifying the effects of various parameters on perturbation inversion was trained using hydrodynamic simulations. Analysis of extensive ANN predictions reveals consistent distributions of dominant modes across different defect types within the examined parameter space. Furthermore, defect height has a greater impact than defect width on the enhancement of nonlinear perturbation wave effects across all modes. These results have important implications for the design of future direct-drive energy targets.