Extreme compression of planetary gases: High-accuracy pressure-density measurements of hydrogen-helium mixtures above fourfold compression

• Published in: Physical review. B 2024-03, Vol.109 (10), Article 104102
• Main Authors: Duwal, Sakun, Clay, Raymond C., Knudson, Marcus D., Boerner, Jeremiah, Cochrane, Kyle, Usher, Joshua, Dolan, Daniel, Farfan, Bernardo, de La Cruz, Chris, Banasek, Jacob, Seagle, Christopher T., Hacking, Richard, Payne, Sheri, Zoller, Charlie, Ahart, Muhtar, Hemley, Russell J.
• Format: Article
• Language: English
• Subjects: Compressive strength; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Continuum mechanics; Critical phenomena; Dynamical phase transitions; First-principles calculations; Phase diagrams; Phase transitions
• ISSN: 2469-9950; 2469-9969
• DOI: 10.1103/PhysRevB.109.104102

Hydrogen (H2) and helium (He), the most abundant elements in the universe, pose a unique challenge in measuring the equation of state of the mixture, owing to their differing physical properties. There remains a need for data with high enough precision to discriminate between existing equation of state (EOS) mix models in order to understand the internal structure of gas-giant planets. Here, we have measured the EOS of precompressed H2- He mixtures at conditions directly relevant to the planetary interiors using hypervelocity gas guns and Sandia’s Z machine with less than 10% uncertainty in density, enabling validation of mixture models. We precompressed 50:50 molar mixtures of H2-He to 0.1–0.2 GPa and directly measured particle velocity (in gas-gun experiments) and shock velocities (in Z-machine experiments). To complement the experimental efforts, we also computed the Hugoniots of precompressed H2-He mixtures using density-functional-theory-based molecular dynamics. Furthermore, we observe approximately 3- to 4.3-fold density compression at pressures up to 44 GPa.