Hugoniot measurements of silicon and radiance transition in shocked silica aerogel

Abstract

Thesis (Ph. D.)--University of Rochester. Department of Physics and Astronomy, 2022This dissertation describes the study of crystalline silicon (Si) and silica (SiO2) aerogel shock-compressed to extreme conditions. Shock waves were generated by laser irradiation and recorded using time-resolved optical diagnostics. The behavior of these materials at high pressure is important to understanding the structure and evolution of terrestrial planets, as well as the performance of ICF capsule designs. Principal Hugoniot and sound speed measurements were performed on silicon to 2100 GPa using high-intensity laser drivers and impedance matching techniques. A change in the shock velocity versus particle velocity (us-up) slope was detected along the fluid silicon principal Hugoniot at 200 GPa. Density functional theory-based quantum molecular dynamics simulations suggest that an increase in ionic coordination and average ionization are coincident with the observed change in slope. Thermodynamic behavior of shock-compressed silica aerogel was studied to test its viability as a bright optical source for high energy density physics experiments. Radiance, reflectance, and shock velocity measurements were performed on singly-shocked SiO2 aerogel at initial densities of 0.3, 0.2, and 0.1 g/cm3 . A change in brightness temperature versus pressure slope is observed along the aerogel Hugoniot, which could be due to radiative, conductive, or microstructure effects. A shock front radiance model is presented to enhance predictive capabilities for shock physics experiments using silica photon sources