Radiative ablation with two ionizing-fronts when opacity displays a sharp absorption edge

TL;DR

This paper investigates how sharp absorption edges in material opacity lead to the formation of a second ionizing front during radiative ablation, affecting inertial confinement fusion and astrophysical phenomena.

Contribution

It provides a detailed mechanism explaining the formation of a second ionizing front caused by sharp opacity edges, which was not previously understood.

Findings

Identification of conditions for the formation of a second I-front

Explanation of how sharp opacity edges generate additional shocks

Implications for fusion capsule design and astrophysical models

Abstract

The interaction of a strong flux of photons with matter through an ionizing-front (I-front) is an ubiquitous phenomenon in the context of astrophysics and inertial confinement fusion (ICF) where intense sources of radiation put matter into motion. When the opacity of the irradiated material varies continuously in the radiation spectral domain, only one single I-front is formed. In contrast, as numerical simulations tend to show, when the opacity of the irradiated material presents a sharp edge in the radiation spectral domain, a second I-front (an edge-front) can form. A full description of the mechanism behind the formation of this edge-front is presented in this article. It allows to understand extra shocks (edge-shocks), displayed by ICF simulations, that might affect the robustness of the design of fusion capsules in actual experiments. Moreover, it may have consequences in various domains of astrophysics where ablative flows occur.