Simultaneous compression and opacity data from time-series radiography with a Lagrangian marker

TL;DR

This paper presents a method to simultaneously determine material opacity and shock states from time-series radiography data using a Lagrangian marker, improving accuracy in high-pressure shock experiments.

Contribution

It introduces a novel approach that leverages Lagrangian markers to constrain opacity and shock parameters, enhancing analysis of converging shock experiments.

Findings

Opacity can be uniquely determined when it varies only on shock heating.

Using markers improves the accuracy of property measurements in high-pressure shocks.

The method is demonstrated with converging shock data in polystyrene at NIF.

Abstract

Time-resolved radiography can be used to obtain absolute shock Hugoniot states by simultaneously measuring at least two mechanical parameters of the shock, and this technique is particularly suitable for one-dimensional converging shocks where a single experiment probes a range of pressures as the converging shock strengthens. However, at sufficiently high pressures, the shocked material becomes hot enough that the x-ray opacity falls significantly. If the system includes a Lagrangian marker, such that the mass within the marker is known, this additional information can be used to constrain the opacity as well as the Hugoniot state. In the limit that the opacity changes only on shock heating, and not significantly on subsequent isentropic compression, the opacity of shocked material can be determined uniquely. More generally, it is necessary to assume the form of the variation of opacity with isentropic compression, or to introduce multiple marker layers. Alternatively, assuming either the equation of state or the opacity, the presence of a marker layer in such experiments enables the non-assumed property to be deduced more accurately than from the radiographic density reconstruction alone. An example analysis is shown for measurements of a converging shock wave in polystyrene, at the National Ignition Facility.