Bulletin of the American Physical Society
16th APS Topical Conference on Shock Compression of Condensed Matter
Volume 54, Number 8
Sunday–Friday, June 28–July 3 2009; Nashville, Tennessee
Session W4: HD-4: Signatures for High Energy-Density Systems |
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Chair: Rip Collins, Lawrence Livermore National Laboratory Room: Hermitage D |
Thursday, July 2, 2009 3:30PM - 3:45PM |
W4.00001: Mixing Rules for Optical and Transport Properties of Warm, Dense Matter Joel Kress, Daniel Horner, Lee Collins Warm, dense matter (WDM) is a regime that requires sophisticated treatment; it is not well described by ideal gas laws or plasma models. A myriad of physical systems fall under the WDM umbrella, from the element ratios in large gas planets and the cooling of white dwarf stars to energy transfer in inertial confinement fusion plasmas and materials under shock compression. Mixtures represent the predominant form of matter throughout the universe and the ability to predict the properties of a mixture, through direct simulation or from convolution of the properties of the constituents is both a challenging prospect and an important goal. Through quantum molecular dynamics (QMD), we can accurately simulate WDM and compute equation of state, transport, and optical properties of such materials, including mixtures, in a self-consistent way from a single simulation. With the ability to directly compute the full mixture properties, we are able to validate mixing rules for combining the optical and dynamical properties of Li and H separately to predict the properties of lithium hydride (LiH). We have looked at two such mixing rules and extend them to morphologies beyond a simple liquid alloy. We have also studied shock compressed methane and polyethylene, where we have looked at the effect of impurities. [Preview Abstract] |
Thursday, July 2, 2009 3:45PM - 4:00PM |
W4.00002: Hard x-rays as a diagnostic tool for warm dense matter Erik Brambrink, H.G. Wei, B. Barbrel, P. Audebert, A. Benuzzi, C. Gregory, M. Rabec le Gloahec, M. Koenig, T. Endo, T. Kimura, R. Kodama, N. Ozaki, T. Boehly, H.-S. Park Laser driven sources producing short bursts of energetic x-rays (10-100 keV) are an important tool to investigate warm dense matter. Radiography, x-ray scattering and x-ray diffraction are the principal tools to measure ionic density, plasma parameters and crystal structure. We studied short-pulse laser-generated hard x-ray (18-60 keV) sources, suitable for radiographs of large samples of dense matter. The spatial and dynamic resolution for different target types and laser parameters have been investigated. A high quality radiographs with good spatial resolution in two dimensions was demonstrated by irradiating free standing thin W wires. We investigated also the influence of the geometry for the quality of the radiograph, which is crucial for the design of experiments probing laser-compressed matter. Finally, we present the application of the x-ray source for the density measurement of shocked iron. [Preview Abstract] |
Thursday, July 2, 2009 4:00PM - 4:15PM |
W4.00003: Observation of Soft-X-ray Superradiance in Hypervelocity (v$>$100 km/s) Impact of Nanoparticles Young Bae Anomalous particle detector signals were discovered by Bae and his colleagues in hypervelocity (v $>$ 100 km/s) impact of nanoparticles, such as water clusters and biomolecules, at Brookhaven National Lab in 1994. The estimated 1-D shock pressure range of the Bae et al's experiments is 20 Mbar -- 2 Gbar. Because the atomic range theory predicts that the nanoparticles cannot penetrate the detector window, thus cannot generate signals, the origin of the signals has been a mystery for more than a decade. In 2007, Winterberg proposed metastable quantum states can be formed with innershell electrons, which would decay by emitting intense x-rays, when atoms are under ``sudden'' compression with pressures in excess of 100 Mbar. The compression in Bae et al.'s experiments can be considered to be ``sudden'', because its time scale (10-100 fs) is much shorter than the ion-electron thermalization time scale ($>$1 ps). The detailed analysis of the anomalous detector signals revealed that they resulted from intense soft-x-rays generated in the nanoparticle impact, and the radiation energies are 75 -- 100 eV in agreement with Winterberg's. The conversion efficiency from the initial nanoparticle kinetic energy to the x-ray radiation energy was as high as 38 {\%}, owing to the Dicke superradiance mechanism, because the size of impact volumes is smaller than the radiation wavelength. [Preview Abstract] |
Thursday, July 2, 2009 4:15PM - 4:30PM |
W4.00004: Attempts of pressure standard material's isentrope measurement and semiconductor/metal sample recovery using laser-driven ramp compression Norimasa Ozaki, Kohei Miyanishi, Tomokazu Sano, Tomoaki Kimura, Takashi Endo, Fumio Kawamura, Akio Hirose, Ryosuke Kodama, Erik Brambrink, Alessandra Benuzzi-Mounaix, Alexandra Diziere, Huigang Wei, Michel Koenig, Tommaso Vinci, Raymond Smith, Osami Sakata, Youichi Sakawa We report preliminary experimental attempts on pressure standard development and on material synthesis/modification using laser-driven ramp compression. Gold and platinum isentropic compression curves are inferred by measuring the free surface velocities of those with different thicknesses. Ramp compressed silicon were recovered at large laser facility, analyzed with synchrotron x-ray diffraction measurements. New peaks appear in the diffraction pattern of the compressed target, which are not found in that of the uncompressed. [Preview Abstract] |
Thursday, July 2, 2009 4:30PM - 5:00PM |
W4.00005: Signatures of multi-Megabar chemistry Invited Speaker: Simple, strongly-bonded dielectrics, such as carbon, hydrogen, and silica, undergo chemical transitions well into the Megabar range giving rise to an extended polymeric fluid regime spread over tens of thousands of degrees. Signatures of such ultra-high pressure bonding changes include gradual increases in optical conductivities, elevated specific heat capacities, and subtle changes in shock compressibility. For initially solid insulators the lower boundary of this reactive, polymeric fluid regime is almost always the melt line indicating that significant bond-breaking is precipitated by melting but continues deep into the fluid phase. More detailed examination of multi-Megabar chemistry has been undertaken through the study of hydrocarbon mixtures and the use of x-ray absorption fine structure measurements. [Preview Abstract] |
Thursday, July 2, 2009 5:00PM - 5:15PM |
W4.00006: Formation and Evolution of a Nonstationary Bounded Self-Governing Electron-Nucleus Collapse in Condensed Targets Vladimir Vysotskii, Stanislav Adamenko We considered peculiarities of the evolution of a region with sharp boundaries that is filled with partially ionized thin spherical layer and is a part of condensed target. The creation of such region can be related to action of impulse electron driver. We defined the conditions such that their fulfilment during the establishment of the equilibrium between the Coulomb attraction of electrons and ions with atom ionization multiplicity Z$_{1}$ and the kinetic pressure of electrons causes both the compression of this region and its ionization to the state with Z$_{2}>$Z$_{1}$. The last leads to further additional compression and ionization. We showed that such avalanche-like ionization and the self-compression of the target happen in the case when the thin spherical ionized layer inside condensed target has drift momentum. Such mechanism can explains the formation of collapse zone and creation of superheavy nuclei observed in ``Proton-21'' Lab [1-3]. 1. Adamenko S. V., Vysotskii V.I.// Found. of Phys. Lett., v. 17, 203 (2004). 2. Adamenko S. V., Vysotskii V.I. //Found. of Phys., v. 34, 1801 (2004). 3. Controlled Nucleosynthesis. Breakthroughs in Experiment and Theory, (Eds: S. Adamenko, F.Selleri, A.van der Merwe), Springer, 2007 [Preview Abstract] |
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