Bulletin of the American Physical Society
18th Biennial Intl. Conference of the APS Topical Group on Shock Compression of Condensed Matter held in conjunction with the 24th Biennial Intl. Conference of the Intl. Association for the Advancement of High Pressure Science and Technology (AIRAPT)
Volume 58, Number 7
Sunday–Friday, July 7–12, 2013; Seattle, Washington
Session W2: HM High Energy Density Materials II |
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Chair: Michael Desjarlais, Sandia National Laboratories Room: Elliott Bay |
Thursday, July 11, 2013 4:00PM - 4:30PM |
W2.00001: Inertial Confinement Fusion as an Extreme Example of Dynamic Compression Invited Speaker: E. Moses Initiating and controlling thermonuclear burn at the national ignition facility (NIF) will require the manipulation of matter to extreme energy densities. We will discuss recent advances in both controlling the dynamic compression of ignition targets and our understanding of the physical states and processes leading to ignition. [Preview Abstract] |
Thursday, July 11, 2013 4:30PM - 5:00PM |
W2.00002: Static experiments above 5 Mbar Invited Speaker: Natalia Dubrovinskaia The impact of high-pressure studies on fundamental physics and chemistry, and especially on the Earth and planetary sciences, has been enormous. While experiments in diamond anvil cells (DACs) at pressures of $\sim$250 - 400 GPa are proven to be very difficult but possible, at higher static pressures any matter has not been investigated so until very recently [Ref. 1]. We have developed a method of synthesis of balls and semi-balls (of 10 to 50 $\mu $m in diameter) made of nanodiamond (with individual nano-particles of linear dimensions below 100 nm) and used them as second-stage or indentor-type anvils in conventional DACs. In experiments on rhenium, osmium, and gold we were able to generate pressures above 650 GPa [Ref. 1] and demonstrated crucial necessity of the ultra-high pressure measurements for accurate determination of the equation of state (EOS) of materials at extreme conditions.\\[4pt] In collaboration with Leonid Dubrovinsky, Bayerisches Geoinstitut, University of Bayreuth; Vitali Prakapenka, University of Chicago; Artem Abukumov, University of Antwerp; and Michael Hanfland; ESRF, Grenoble.\\[4pt] [1] L. Dubrovinsky, N. Dubrovinskaia, V. Prakapenka, A. Abakumov. Implementation of micro-ball nanodiamond anvils for high-pressure studies above 6 Mbar. \textit{Nat. Commun.} 3:1163 doi: 10.1038/ncomms2160, 2012. [Preview Abstract] |
Thursday, July 11, 2013 5:00PM - 5:30PM |
W2.00003: Isochoric heating using proton beams and shock compression generated by UHI lasers Invited Speaker: Markus Roth Material conditions in the Warm Dense Matter (WDM) regime are of great interest for high energy density physics, the development of controlled thermonuclear fusion and astrophysics. Each experiment involving high energy deposition will be strongly affected by the sample's changed behavior in the WDM regime. In particular, carbon is an interesting material for warm dense matter studies, as it is accessible experimentally since carbon samples can easily be manufactured and handled in the laboratory. Due to its low number of electrons, a number of theoretical and numerical techniques, including ab-initio simulations, allow for the description of its properties within the computational resources available today. Additionally, the solid-liquid phase transition of carbon is in the warm dense matter regime and may play a major role in the physics of ice giants like Neptune and Uranus [1, 2] and white dwarfs [3]. This transition is poorly understood so far and further investigation is needed [4]. In fact, the solid-liquid phase transition on the graphite Hugoniot has never been measured reliably so far. A recent new option is the use of x-rays which are able to access the processes inside the sample. In comparison to radiography x-ray scattering cannot only measure the propagation of a shock but also the microscopic structure inside the sample [5, 6, 7]. Thus, strong changes in the structure due to the phase transitions induced by shock or isochoric heating can be measured directly. The creation of fluid carbon requires a rapid energy input, preferably into a large volume. Ion beams are a unique tool for that task as they deposit their energy deep in the target resulting in a uniform heating profile. Ultra-short proton bursts generated by high-intensity laser beams match both the high particle number and the short pulse length required to create fluid carbon without noticeable expansion. In this talk we present the measurement of the microscopic structure change of graphite in a heated sample and in a laser driven shock with x-ray scattering. This method was first applied for the carbon solid-liquid phase transition at lower pressure in a proof-of-principle experiment where the isochoric heating was realized by laser-accelerated protons [8]. However, in this first experiment only the relative increase of the total scattering signal was measured. It was not possible to distinguish between the elastic and inelastic features. In the experiment presented in this talk, we have obtained frequency-resolved scattering spectra, which allow to study the evolution of both the elastic and the inelastic features separately. \\[4pt] [1] W. B. Hubbard et al., Science 253, 648 (1991) [2] S. Stanley and J. Bloxham, Nature 428, 151 (2004) [3] P. Dufour et al. Nature 450, 522 (2007) [4] A. A. Correa, S. A. Bonev and G. Galli, Proc. Natl. Acad. Sci. USA 103, 1204 (2006) [5] S. H. Glenzer and R. Redmer, Rev. Mod. Phys. 81, 1625 (2009) [6] E. Garcia Saiz et al., Nature Physics 4, 940 (2008). [7] K. W\"{u}nsch, J. Vorberger, and D.O. Gericke, Phys. Rev. E 79, 010201(R) (2009). [8] A. Pelka, G. Gregori, D. O. Gericke et al., Phys. Rev. Lett. 105, 265701 (2010) . [Preview Abstract] |
Thursday, July 11, 2013 5:30PM - 5:45PM |
W2.00004: Astrophysical experiments at a gigabar on the National Ignition Facility A. Kritcher, D.C. Swift, T. Doeppner, J.A. Hawreliak, J. Eggert, G.W. Collins, S. Glenzer, R. Falcone, P. Neumayer We have now demonstrated a capability at NIF to produce accurate equation of state (EOS) measurements on matter into the gigabar regime. Work so far has focused on CH, but with further development it will be possible to study other materials, in particular of higher Z. As well as being relevant to high-pressure engineering systems such as inertial confinement fusion, we can address key problems in astrophysics. Gigabar-scale pressures occur within massive exoplanets, and experimentally-constrained EOS measurements are essential to interpret exoplanet observations in terms of internal structures. This research provides important constraints for assessments of dark matter, by improving estimates of the total amount of baryonic mass for a given density of luminous (stellar) mass, because the ratio of non-luminous to luminous mass depends on the upper mass limit of brown dwarfs, which depends sensitively on the EOS. We are also able in NIF experiments to deduce the opacity along the shock Hugoniot, which is a necessary component in studies of stellar structure and evolution. [Preview Abstract] |
Thursday, July 11, 2013 5:45PM - 6:00PM |
W2.00005: Thermodynamic and transport properties along Jupiter's adiabat Martin French, Andreas Becker, Winfried Lorenzen, Nadine Nettelmann, Mandy Bethkenhagen, Johannes Wicht, Thomas Mattsson, Ronald Redmer Accurate knowledge about the behavior of the major constituents, hydrogen and helium, is required to model and understand the interior of Jupiter. Transport properties like the thermal and electrical conductivity as well as the viscosity are particularly interesting to examine, since their behavior changes drastically at the transition from the dense nonideal plasma to the molecular fluid. Here we use \textit{ab initio} molecular dynamics simulations based on density functional theory to calculate equilibrium and transport properties of the warm dense H-He mixture. In particular, we present results [1] for thermodynamic material properties, the shear and longitudinal viscosity, the electrical and the thermal conductivity in hydrogen-helium mixtures along the isentrope of Jupiter, Our results cover the range from the outer molecular regions (2000 K, 5 kbar) to the core-mantle boundary (19000 K, 40 Mbar). These new data will lead, e.g., to significant improvements in understanding the origin and shape of the magnetic field of Jupiter.\\[4pt] [1] M. French, A. Becker, W. Lorenzen, N. Nettelmann, M. Bethkenhagen, J. Wicht, R. Redmer, Astrophys. J. Suppl. Ser. 202, 5 (2012). [Preview Abstract] |
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