Engineering topics

Hamel, S.

Publications and source records attributed to Hamel, S..

5 records

DOE OSTI2024

Measurements of K-edge and L-edge extended x-ray absorption fine structure at the national ignition facility (invited)

High-energy-density laser facilities and advances in dynamic compression techniques have expanded access to material states in the Terapascal regime relevant to inertial confinement fusion, planetary science, and geophysics. However, experimentally determining the material temperature in these extreme conditions has remained a difficult challenge. Extended X-ray Absorption Fine Structure (EXAFS), referring to the modulations in x-ray absorption above an absorption edge from photoelectrons’ interactions with neighboring atoms, has proven to be a versatile and robust technique for probing material temperature and density for mid-to-high Z elements under dynamic compression. The current platform at the National Ignition Facility has developed six configurations for EXAFS measurements between 7 and 18 keV for different absorption edges (Fe K, Co K, Cu K, Ta L3, Pb L3, and Zr K) using a curved-crystal spectrometer and a bright, continuum foil x-ray source. Here, in this work, we describe the platform geometry, x-ray source performance, spectrometer resolution and throughput, design considerations, and data in ambient and dynamic-compression conditions.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Evidence for dissociation in shock-compressed methane

Theory and experiments show that with increasing pressure, the chemical bonds of methane rearrange, leading to the formation of complex polymers and then to dissociation. However, there is disagreement on the exact conditions where these changes take place. In this study, methane samples were precompressed in diamond-anvil cells and then shock compressed to pressures reaching 400 GPa, the highest pressures yet explored in methane. Furthermore, the results reveal a qualitative change in the Hugoniot curve at 80-150 GPa, which is interpreted as a signature of dissociation based on thermodynamic calculations and theoretical predictions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

A Limited-Ranged Two-Phase Iron Equation of State Model

This report describes the construction of a two-phase EOS for Fe that includes both (hcp) and liquid phases, and which is meant to be valid over the restricted range: V ϵ [4 : 7] °A 3 /atom, and T ϵ [1000 : 20000] K. It was recently used as the basis for a theoretical study of liquid → solid phase transformation kinetics in Fe which appeared in the Supplemental Material for a paper describing a series of NIF shock + ramp compression experiments aimed at constraining the high-P melt curve of Fe.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2021

Implications of the iron oxide phase transition on the interiors of rocky exoplanets

The discovery of an extraordinary number of extrasolar planets, characterized by an unexpected variety of sizes, masses and orbits, challenges our understanding of the formation and evolution of the planets in the Solar System and the perception of the Earth as the prototypical habitable world. Many exoplanets appear to be rocky and yet more massive than the Earth, with expected pressures and temperatures of hundreds of gigapascal and thousands of Kelvin in their deep interiors. At these conditions, the properties of bridgmanite and ferropericlase, expected to dominate their mantles, are largely unconstrained, limiting our knowledge of their interior structure. Here we used nano-second X-ray diffraction and dynamic compression to experimentally investigate the atomic structure and density of iron oxide (FeO), one of the end-members of the (Mg,Fe)O ferropericlase solid solution, up to 700 GPa, a pressure exceeding the core–mantle boundary of a 5 Earth masses planet. Our data document the stability of the high-pressure cesium-chloride B2 structure above 300 GPa, well below the pressure required for magnesium oxide (MgO) to adopt the same phase. These observations, complemented by the calculation of the binary MgO–FeO phase diagram, reveal complex stratification and rheology inside large terrestrial exoplanets.

58 GEOSCIENCES↗

DOE OSTI2020

Reduction of electron-phonon coupling in warm dense iron

The electron-ion relaxation dynamics in warm dense iron were investigated by time-resolved x-ray absorption near-edge spectroscopy (XANES). A novel analysis, combining ab initio density functional theory (DFT) and two temperature model (TTM) simulations, was developed to calculate the x-ray absorption spectra as a function of delay time. Here we present experimental evidence of changes at the XAS L3 edge of iron that are consistent with the reduction of the electron-phonon coupling under warm dense matter conditions. The experimental results are in agreement with the model that takes both the electron ($T_e$) and the ion temperature ($T_i$) dependence of the thermophysical properties into consideration, while models where either constant electron-phonon coupling factor (G) or only $T_e$- dependent G are used do not agree with the observed relaxation dynamics of iron.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗