Species stratification and suprathermal ion velocity separation driven by an electrostatic collisionless shock inside an ICF hohlraum

Abstract In indirect-drive inertial confinement fusion, there are significant non-equilibrium kinetic effects that deviate from hydrodynamic descriptions in the region of relatively high temperature and low density. Crucially, the complex interfacial kinetic process can alter the plasma properties at the interface between the high- Z hohlraum inner wall plasma and the low-density fill-gas plasma, thereby affecting laser transport and energy deposition processes. The kinetic collisionless shock wave can form at the wall-gas interface. In this work, we investigated the multi-ion-species effects during the formation and propagation of the collisionless shock driven by the expansion of high- Z gold (Au) plasma into the rarefied deuterium–hydrogen gas mixture using one-dimensional implicit Particle-in-Cell simulations. The results reveal that the spatio-temporal evolution of the electrostatic potential approaches a steadily propagating two-step rise pattern due to its interplay with the plasma mixtures. The downstream ion-species stratification attributed to electro-diffusion was explored and found to increase the shock velocity compared to the single-ion species cases under identical initial temperature and electron densities. Additionally, the characteristic two-step rise potential structure would induce the anomalous velocity distributions of reflected suprathermal ions relevant to experiments. A quantitative relationship is established between shock characteristics and the velocity distribution discrepancies of reflected H and D ion species. These findings advance the understanding of electrostatic collisionless shock physics in multi-ion-species plasmas and provide critical insights for assessing the hohlraum plasma conditions.