Equation of State and Electrical Conductivity of Helium at High Pressures and Temperatures

Details Equation of State and Electrical Conductivity of Helium at High Pressures and Temperatures Equation of State and Electrical Conductivity of Helium at High Pressures and Temperatures

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.p51b1424m&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #P51B-1424

Physics

5700 Planetology: Fluid Planets, 5705 Atmospheres: Evolution, 5724 Interiors (8147), 5754 Physical Properties Of Materials

Scientific paper

Helium, the second-most abundant element in the universe and giant planets, is expected to metallize at much higher pressures and temperatures than the most abundant element, hydrogen. The difference in chemical-bonding character, between insulator and metal, is expected to make hydrogen-helium mixtures immiscible throughout large fractions of planetary interiors, and therefore subject to gravitational separation contributing significantly to the internal dynamics of giant planets. Using laser-driven shock waves on samples pre-compressed in high-pressure cells, we have obtained the first measurements of optical reflectivity from the shock front in helium to pressures of 146 GPa. The reflectivity exceeds 5% above \ensuremath{\sim} 100 GPa, indicating high electrical conductivity. By varying the initial pressure (hence density) of the sample, we can access a much wider range of final pressure-temperature conditions than is possible in conventional Hugoniot experiments. Our work increases by nine-fold the pressure range of single-shock measurements, in comparison with gas-gun experiments, and yields results in agreement with the Saumon, Chabrier and Van Horn (1994) equation of state for helium. This changes the internal structures inferred for Jupiter-size planets, relative to models based on earlier equations of state (e. g., SESAME).

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