HR: 0800h
AN: P51B-1424    [Abstracts]
TI: Equation of State and Electrical Conductivity of Helium at High Pressures and Temperatures
AU: * McWilliams, R S
EM: rmcw@eps.berkeley.edu
AF: Department of Earth and Planetary Science, 307 McCone Hall, University of California Berkeley, Berkeley, CA 94720 United States
AU: * McWilliams, R S
EM: rmcw@eps.berkeley.edu
AF: Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94550 United States
AU: Eggert, J H
EM: eggert1@llnl.gov
AF: Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94550 United States
AU: Loubeyre, P
EM: paul.loubeyre@cea.fr
AF: D\'{e}partement de Physique Th\'{e}orique et Applications, Commissariat \`{a} l'Energie Atomique , Bruyeres-le-Chatel, 91680 France
AU: Brygoo, S
EM: stephanie.brygoo@cea.fr
AF: D\'{e}partement de Physique Th\'{e}orique et Applications, Commissariat \`{a} l'Energie Atomique , Bruyeres-le-Chatel, 91680 France
AU: Collins, G
EM: collins7@llnl.gov
AF: Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94550 United States
AU: Jeanloz, R
EM: jeanloz@berkeley.edu
AF: Department of Earth and Planetary Science, 307 McCone Hall, University of California Berkeley, Berkeley, CA 94720 United States
AB: 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).
DE: 5700 PLANETOLOGY: FLUID PLANETS
DE: 5705 Atmospheres--evolution
DE: 5724 Interiors (8147)
DE: 5754 Physical properties of materials
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting