Mark E. Foord

Equation of state measurements of hydrogen isotopes on Nova

High intensity lasers can be used to perform measurements of materials at extremely high pressures if certain experimental issues can be overcome. We have addressed those issues and used the Nova laser to shock-compress liquid deuterium and obtain measurements of density and pressure on the principal Hugoniot at pressures from 300 kbar to more than 2 Mbar. The data are compared with a number of equation of state models. The data indicate that the effect of molecular dissociation of the deuterium into a monatomic phase may have a significant impact on the equation of state near 1 Mbar.

Idealized slab plasma approach for the study of warm dense matter

Recently, warm dense matter has emerged as an interdisciplinary field that draws increasing interest in plasma physics, condensed matter physics, high pressure science, astrophysics, inertial confinement fusion, as well as material science under extreme conditions. To allow the study of well-defined warm dense matter states, we introduced the concept of idealized slab plasma (ISP) that can be realized in the laboratory via (1) the isochoric heating of a solid and (2) the propagation of a shock wave in a solid. The application of this concept provides new means for probing AC conductivity, equation of state, ionization, and opacity. These approaches are presented here using results derived from numerical simulations.

Interferometric investigation of femtosecond laser-heated expanded states

Simultaneous temporally and spatially resolved measurements of the phase change and reflectivity of S- and P-polarized femtosecond laser probes are obtained from hot expanded states produced by femtosecond laser heating of a solid aluminum target. The combined set of data provides an integral test of equation-of-state models in a regime up to 10 Mbar and densities of 0.01–1 times solid. The results suggest that target stoichiometry at the few A level should be considered in the analysis of phase and reflectivity measurements in such experiments.

Equation of State and Material Property Measurements of Hydrogen Isotopes at the High-Pressure, High-Temperature, Insulator-Metal Transition

A high-intensity laser was used to shock compress liquid deuterium to pressures between 0.22 and 3.4 megabars (Mbar). Shock density, pressure, and temperature were determined using a variety of experimental techniques and diagnostics. This pressure regime spans the transformation of deuterium from an insulating molecular fluid to an atomic metallic fluid. Data reveal a significant increase in compressibility and a temperature inflection near 1 Mbar, both indicative of such a transition. Single-wavelength reflectivity measurements of the shock front demonstrated that deuterium shocked above {approx}0.5 Mbar is indeed metallic. (c) 2000 The American Astronomical Society.

Interferometric and Chirped Optical Probe Techniques for High-Pressure Equation-of-State Measurements*

We present experimental work exploring displacement and velocity interferometry as high spatial and temporal resolution diagnostics for measuring target preheat and the speed, planarity, and steadiness of a shock wave. A chirped pulse reflectometry experiment is also proposed as a frequency domain alternative for shock speed measurements. These techniques fill a need for high-precision diagnostics to derive accurate laboratory-based equation-of-state data at shock wave-driven pressures directly relevant to astrophysical systems. The performance of these optical laser probe techniques may exceed conventional passive techniques such as temporally streaked recording of optical emission upon shock breakout or side-on streaked X-ray radiography. Results from Nova laser and high-intensity ultrashort pulse experiments are presented.

Equation of state measurements of D2 on nova

Hugoniot measurements of liquid molecular deuterium were made using laser-driven shocks. The equation-of-state data are in agreement with the dissociation model (AIP)

Equation of state measurements of D2on nova

Hugoniot measurements of liquid molecular deuterium were made using laser-driven shocks. The equation-of-state data are in agreement with the dissociation model (AIP)