Nonlinear evolution of hydrodynamic instabilities seeded by the isolated internal defect in HDC capsules

Abstract Achieving fusion ignition and higher gain requires substantial heating and compression of thermonuclear fuel. However, internal defects in the capsule can disrupt this process by seeding nonlinear hydrodynamic instabilities during implosion. We systematically analyze the evolution of isolated internal defects at various locations within a planar high-density carbon (HDC) capsule driven by x-ray radiation. Our results show that defect evolution varies significantly based on location due to the differing speeds of the shockwave and ablation front. Front-located defects are influenced by both the shockwave and the ablation front, leading to lateral disturbances and vortex traces as the shockwave passes through. This interaction causes an inverted density distribution, resulting in defects on the central axis evolving into spike-like structures. Mid-located defects encounter the shockwave before the ablation front, resulting in vorticity deposition and vortex pair formation, which interact with the ablation front in a positive feedback loop, enhancing nonlinear growth. Rear-located defects are reached by a rarefaction wave before the ablation front, causing the defects to accelerate ahead while the ablation front maintains a stable structure. Additionally, defects with varying initial disturbance amplitudes at the same position exhibited a certain degree of self-similarity in their evolution. These results provide crucial theoretical insights and numerical simulations for understanding the complex mechanisms by which shockwaves and ablation fronts influence defect evolution within HDC capsules.