Systematic investigation of density incrustation at low-Z/high-Z interfaces in HED systems

M Das,C Bhattacharya

doi:10.1063/5.0042170

Abstract

A systematic investigation of the phenomenon of density incrustation was done by performing radiation hydrodynamics simulations at the interface of low-Z and high-Z materials. In this work, a high-Z material was maintained at a very high temperature compared to an adjacent low-Z material. This led to propagation of heat wave and shock wave into the low-Z medium. Rarefaction of the high-Z interface was arrested by a shock compressed low-Z medium. A sharp increase in density (density incrustation) was observed in rarefying high-Z plasmas at the interface. Density incrustation was not observed when rarefaction in the high-Z material occurred in the absence of the adjacent low-Z medium or when the radiation drive was incident on the low-Z material transmitting heat wave and shock wave into the high-Z material. The effect of the radiation drive, opacity, and equation of state on density incrustation at the interfaces of different high-Z (Au, U, and Pb) and low-Z (CH, Be, and Al) materials was studied. We observed that the height of incrustation depends on the temperature of the radiation drive, density, and opacity of the low-Z arrester material. This work has significance in the design of inertial confinement fusion systems wherein peaking of density in rarefying high-Z plasmas increases the Atwood number, contributing toward the growth of Rayleigh–Taylor instability at the interface.

Highlights

Radiation hydrodynamics governs several physical phenomena observed in high energy density (HED) systems, such as inertial confinement fusion (ICF), stellar interiors, and laser–matter interactions.1,2 In HED systems, we often encounter interfaces comprising different materials, e.g., sandwich targets in Hohlraums,3,4 foam confined targets for ablation experiments,5–7 core regions of very massive stars, and gold coated direct drive ICF capsules.8,9 The interplay of hydrodynamic motion and radiation transport at these interfaces gives rise to several interesting physical phenomena
We explored situations where there occurs an interplay between radiation transport and hydrodynamics at the interface of dissimilar materials, but the phenomenon of density incrustation does not occur
In order to further investigate the cause of appearance/nonappearance of incrustation in density at interfaces, we presented the radial distribution of pressure, density, and temperature in the a high-Z Hohlraum material (Au)–CH system for both cases

Summary

Introduction

Radiation hydrodynamics governs several physical phenomena observed in high energy density (HED) systems, such as inertial confinement fusion (ICF), stellar interiors, and laser–matter interactions. In HED systems, we often encounter interfaces comprising different materials, e.g., sandwich targets in Hohlraums, foam confined targets for ablation experiments, core regions of very massive stars, and gold coated direct drive ICF capsules. The interplay of hydrodynamic motion and radiation transport at these interfaces gives rise to several interesting physical phenomena. Hydrodynamic motion dictates the pressure that remains constant over the time scale when temperature drops across the interface due to radiation transport This leads to a sharp increase in density at the interface termed density incrustation. Cooling layers are observed in radiative shock experiments where a shock heated downstream material radiates energy to a cold upstream material, resulting in a rise in temperature at the shock front.. Cooling layers are observed in radiative shock experiments where a shock heated downstream material radiates energy to a cold upstream material, resulting in a rise in temperature at the shock front.2,11,12 Both density incrustation and radiative shocks are accompanied by the formation of cooling layers, the two phenomena differ drastically in their origin and characteristics Cooling layers are observed in radiative shock experiments where a shock heated downstream material radiates energy to a cold upstream material, resulting in a rise in temperature at the shock front. both density incrustation and radiative shocks are accompanied by the formation of cooling layers, the two phenomena differ drastically in their origin and characteristics

Methods

Results

Conclusion