Instability seeding mechanisms at the fuel–ablator interface due to internal defects

Source abstract

During the fabrication process of inertial confinement fusion targets, the ablation material often contains near-vacuum “voids.” The interaction between the shock waves generated by laser or x-ray ablation and these voids results in hydrodynamic instabilities, which significantly hinder uniform target compression and degrade implosion performance. In the present paper, we systematically analyze the evolution mechanisms of isolated internal defects within a planar high-density carbon (HDC) capsule under the impact of shock waves driven by a high-energy laser, and the subsequent development of material interface perturbations. The focus is on two critical stages: the interaction between the shock wave and the “voids” and the interaction between the deformed transmitted shock wave and the flat HDC/DT interface. The results indicate that baroclinic effects generate jets and split the defect into two parts. Interactions between the isolated defect and nonlinear pressure waves create symmetrically positioned local high-pressure zones that deposit vorticities on the material interface. Interface perturbations develop as a result of these vorticities. The vertical scale of perturbations ultimately grows to 4–5 times the original defect diameter, primarily driven by secondary jets from these high-pressure zones. In addition, this paper further investigates how the Atwood number between the defect and surrounding material, as well as the varying defect distances from the material interface, impact perturbation development. Understanding these mechanisms is essential for improving HDC target design and fabrication, enhancing implosion performance, and advancing the efficiency and effectiveness of inertial confinement fusion.