Investigation of diffusion-driven plasma mixing in the context of indirect drive inertial confinement fusion

In indirect-drive inertial confinement fusion (ICF), plasma mixing between high-Z hohlraum plasmas and low-Z filling plasmas significantly affects local plasma conditions, thereby influencing the evaluation of laser plasma instabilities (LPI). This study investigates the diffusion-driven mixing between hohlraum-ablated Au plasmas and filling C5H12 plasmas using one-dimensional particle-in-cell simulations. We find that ion–ion collisions slow the diffusion of ions, rendering Au ions sub-diffusive, while C and H ions remain super-diffusive. Due to their lower collisionality, H ions diffuse faster into Au regions than C ions, leading to a distinct separation between C and H ions at the interface. Compared with collisionless scenarios, the electrostatic shock wave persists at the plasma interface even in the presence of collisions, though collisions notably reduce its electric field amplitude and propagation velocity. Systematic analyses show that laser irradiation and plasma flow have minimal influence on ion mixing speed compared to diffusion-driven mechanisms, whereas inhomogeneous density profiles substantially restrict ion diffusion from low density to high density regions. By incorporating realistic hohlraum plasma conditions from radiation hydrodynamic models into our simulations, we demonstrate the persistent dominance of diffusion-driven ion mixing. Further theoretical calculations indicate that the penetration of H and C into Au plasmas suppresses stimulated Brillouin scattering within the mixing layer. This highlights the importance of incorporating ion mixing processes into LPI modeling for more accurate predictions in ICF experiments.