Effect of equation of state on laser imprinting by comparing diamond and polystyrene foils

H Kato,Y Hironaka,M Nakai,H Azechi,K Shigemori,T Sakaiya,T Ueda,H Nagatomo,K Shimizu,H Terasaki

doi:10.1063/1.5018906

Abstract

We present herein a comprehensive study of how the equation of state affects laser imprinting by nonuniform laser irradiation of an inertial fusion target. It has been suggested that a stiffer and denser material would reduce laser imprinting based on the equation of motion with pressure perturbation. We examine the detailed temporal evolution of the imprint amplitude by using the two-dimensional radiation hydrodynamic simulation PINOCO-2D for diamond, which is a candidate stiff-ablator material for inertial fusion targets. The simulated laser imprinting amplitude is compared with experimental measurements of areal-density perturbations obtained by using face-on x-ray backlighting for diamond and polystyrene (PS) (the latter as a reference). The experimental results are well reproduced by the results of the PINOCO-2D simulation, which indicates that the imprinting amplitude due to nonuniform irradiation (average intensity, 4.0 × 1012 to 5.0 × 1013) differs by a factor of two to three between diamond and PS. The difference in laser imprinting is mainly related to the material density and compressibility. These parameters are key factors that determine the laser imprinting amplitude.

Highlights

The Rayleigh–Taylor instability (RTI) is a hydrodynamic instability caused by gravity and is generally understood as a basic phenomenon in nature.1,2 The RTI occurs at the interface between accelerating materials with different densities
We present a comprehensive study of how the equation of state affects laser imprinting by nonuniform laser irradiation of an inertial fusion target
We examine the detailed temporal evolution of the imprint amplitude by using the two-dimensional radiation hydrodynamic simulation PINOCO-2D for diamond, which is a candidate stiff-ablator material for inertial fusion targets

Summary

Introduction

The Rayleigh–Taylor instability (RTI) is a hydrodynamic instability caused by gravity and is generally understood as a basic phenomenon in nature. The RTI occurs at the interface between accelerating materials with different densities. In inertial confinement fusion (ICF) targets, the RTI and related hydrodynamic mixing are the most crucial factors determining thermonuclear ignition during the implosion timeline. Numerous studies of the RTI and related hydrodynamic instabilities have been done based on this understanding.. Because the RTI makes small perturbations at the target surface grow exponentially over time, initial perturbations at the ICF target surface should be as small as possible. Such surface perturbations are mainly due to two factors: (i) the surface roughness resulting from target fabrication and (ii) imprinting due to nonuniform laser irradiation. Numerous efforts have been made to understand the physics of laser imprinting.

Objectives

Results

Conclusion