Effect of spherical geometrical convergence on the nonlinear bubble evolution of hydrodynamic instabilities in laser-driven implosion

This study investigates the nonlinear evolution of hydrodynamic instabilities seeded by isolated internal defects during the early stages of inertial confinement fusion implosions, with a focus on the effect of spherical geometrical convergence. Through comprehensive numerical simulations, we examine the interaction between the shock wave and defects in spherical capsules with varying initial radii. Key findings reveal that spherical geometrical convergence plays a critical role in the evolution of both vorticity distribution and perturbation growth. This effect can inhibit the positive feedback mechanism of the vortex, which was previously reported in Liu et al. [Phys. Plasmas 30, 042302 (2023)]. Specifically, spherical geometrical convergence exerts a notable effect: it enhances the compression of the capsule and accelerates the inward motion of the vortex rings. This enhanced compression and accelerated vortex motion mitigate perturbations of the ablation front when the defects are far from the capsule surface. However, when defects are near the capsule surface, the effect of spherical geometrical convergence reverses; instead, it enhances perturbations at the ablation front. Quantitative analysis of the temporal evolution of the vortex ring major radius and distance from the ablation front further elucidates the underlying physical processes. These results provide critical insights into hydrodynamic instabilities in spherical geometries and performance degeneration factors of capsules with different scales.