Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session J4: Geophysics and Planetary Science IV: Tom Ahrens Memorial |
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Chair: Sarah Stewart, Harvard University Room: Renaissance Ballroom C |
Tuesday, June 28, 2011 11:00AM - 11:15AM |
J4.00001: Professor Thomas J. Ahrens and Shock Wave Physics in Russia Vladimir E. Fortov, Gennady I. Kanel Since his earlier works on the equations of state and dynamic mechanical properties of rocks and other materials Prof. T.J. Ahrens furnished large influence on development of the shock wave physics in Russia. He always demonstrates a choice of excellent problems and a level of productivity in the field of shock compression science which is unparalleled. In recognition of his great contribution into science and international scientific collaboration Prof. Ahrens has been elected in Russian Academy of Sciences as its foreign member. In the presentation, emphasis will be done on the Comet Shoemaker-Levy project in which we had fruitful informal collaboration, on the problem of wide-range equations of state, and on stress relaxation at shock compression of solids. [Preview Abstract] |
Tuesday, June 28, 2011 11:15AM - 11:30AM |
J4.00002: Shock compression of preheated silicate liquids: 30 years of progress Paul Asimow Tom Ahrens and his students pioneered, beginning around 1981, the technique of determining silicate liquid equations of state for geophysical applications using shock compression of pre-heated, encapsulated samples. In the last decade, we have ported this technique to the Caltech two-stage light gas gun and extended several pre-heated liquid Hugoniots to over 125 GPa. We now have enough compositions studied to perform several tests of the theory of linear mixing or, assuming linear mixing, to describe any liquid in the five-component CaO-MgO-FeO-Al$_{2}$O$_{3}$-SiO$_{2}$ system. This data allows us to identify liquid compositions likely to be negatively or neutrally buoyant in the lower mantle and to form a preliminary description of the dynamics of partial melting of solid lower mantle or initial crystallization of a deep mantle magma ocean. The most robust and surprising feature of all studied liquids, which places very strong constraints on microscopic models for silicate liquid compression behavior, is anomalous increase of the Gr\"uneisen parameter upon compression, with remarkably consistent q = dln$\gamma$/dlnV = -1.75$\pm$0.25. [Preview Abstract] |
Tuesday, June 28, 2011 11:30AM - 11:45AM |
J4.00003: Thermodynamics of MgO shocked to 250 GPa and 9000~K O.V. Fat'yanov, P.D. Asimow, T.J. Ahrens Plate impact experiments in the 200-250 GPa pressure range were done on $<$100$>$ single-crystal MgO preheated before compression to 1850 K. Hot Mo(driver)-MgO targets were impacted with Ta flyers launched by the Caltech two-stage light-gas gun up to 7.5 km/s. Radiative temperatures and shock velocities were measured with 3-5\% and 1-2\% respective uncertainty by a 6-channel pyrometer with 3 ns time resolution, over 500-900 nm spectral range. MgO shock front reflectivity was determined in additional experiments at 220 and 250 GPa using $_{\verb1~1}$50/50 high-temperature sapphire beamsplitters. Shock temperatures and preheated MgO Hugoniot data reported here are in good agreement with the corresponding values calculated using Mie-Gr\"{u}neisen equation of state with $\gamma_0$=1.4 and constant $\gamma/V$. Our experiments showed no evidence of MgO melting up to 250 GPa and 9.2 kK. The highest shock temperatures exceed the extrapolated melting curve of Zerr \& Boehler by $>$3000 K at 250 GPa, which seems too much for any realistic superheating. [Preview Abstract] |
Tuesday, June 28, 2011 11:45AM - 12:00PM |
J4.00004: Quasi-Isentropic Compression of Iron to 268 GPa at the Omega Laser Facility Jue Wang, Raymond Smith, Jon Eggert, Javier Montoya, Dave Braun, Thomas Boehly, Gilbert Collins, Thomas Duffy Development of techniques for laser-based quasi-isentropic ramp compression in planetary materials has applications to understanding the structure and dynamics of the interiors of planets both within and outside our solar system. Ramp compression which achieves high compression at relatively modest temperatures can be used to extract quasi-isentropic equation-of-state data and study solid-solid phase transitions. An experimental platform for ramp loading of iron (Fe) has been established and tested in experiments at the Omega Laser Facility. A spatially planar ($\Delta $t/t = 0.9{\%}) ramp wave drive has been achieved in iron (Fe) stepped samples to peak stress above 1 Mbar over 10-ns time scales. The $\alpha -\varepsilon $ transition is overdriven by an initial shock pulse of $\sim $81.4 GPa followed by ramp compression. Through the use of Lagrangian analysis on the measured wave profiles, stress-density states in iron have been determined to pressures of 268 GPa. Use of an initial shock followed by a ramp will allow a wider range of P-T states to be accessed via ramp compression. [Preview Abstract] |
Tuesday, June 28, 2011 12:00PM - 12:15PM |
J4.00005: Serpentine Hugoniot and wave profiles of DISAR Chuanmin Meng, Hongliang He, Toshimori Sekine The previous Hugoniot measurements on serpentine have indicated two phase transitions at pressures of 40 GPa and 125 GPa. We investigated detailed wave profiles in order to see how the shock properties change with the phase transitions and to understand what phase appears after the transition. Our measured profiles of DISAR on natural antigorite have no two-wave structure, but single wave structures appear up to 130 GPa. However the onset slope of adiabatic release after the Hugoniot state changed with the Hugoniot pressure. This change will be discussed in terms of the phases present at the time of Hugoniot state. [Preview Abstract] |
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