Bulletin of the American Physical Society
19th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 60, Number 8
Sunday–Friday, June 14–19, 2015; Tampa, Florida
Session L2: Experimental Developments VII: Diagnostic Development |
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Chair: Dana Dlott, University of Illinois at Urbana-Champaign, Joseph Zaug, Lawrence Livermore National Laboratory Room: Grand F |
Tuesday, June 16, 2015 3:45PM - 4:00PM |
L2.00001: Thin metal thermistors for shock temperature measurements of polymers N.E. Taylor, D.M. Williamson, A. Picard, L.K. Cunningham, A.P. Jardine Equations of state can be used to predict the relationship between pressure, volume and temperature. However, in shock physics, they are usually only constrained by experimental observations of pressure and volume. Direct observation of temperature in a shock is therefore valuable in constraining equations of state. Bloomquist and Sheffield (1980, 1981) and Rosenberg and Partom (1984) have attempted such observations in poly(methyl methacrylate) (PMMA). However, their results disagree strongly above 2 GPa shock pressure. The present authors previously presented an improved fabrication technique, to examine this outstanding issue. This technique made use of the fact that the electrical resistivity of most metals is a known function of both pressure and temperature. By fabricating a thin metal thermistor gauge and measuring its change in resistance during a shock experiment of known pressure, its temperature can be recovered. Heat transfer into the gauge depends strongly on the gauge dimensions and the thermal conductivity of the shocked PMMA. Here we present several improvements to the technique. By varying the gauge thickness over the range 100~nm to $10\,\mu$m we assess the heat transfer into the gauge. [Preview Abstract] |
Tuesday, June 16, 2015 4:00PM - 4:15PM |
L2.00002: Calibration of fiber-optic shock pyrometer using high-power coiled tungsten lamp O.V. Fat'yanov, P.D. Asimow Comparison of all known calibration sources indicates that coiled standards of spectral irradiance, despite their very non-uniform brightness, are currently the best practical choice for accurate shock temperature measurements above 3000 K by optical pyrometry. We review all three documented methods of shock pyrometer calibration to a coiled lamp and show that only one technique, with no fiber-optics employed, is free of major radiometric errors. We report the development of a new, accurate to 5\% and precise to 1-1.5\% calibration procedure for the modified Caltech 6-channel, 3-ns temporal resolution combined open beam and fiber-coupled instrument. A designated central area of an 0.7x demagnified image of 900 W coiled-coil lamp filament is used, cross-calibrated against a NIST-traceable tungsten ribbon lamp. The results of two slightly different cross-calibrations are reported and the procedure to characterize the difference between the static and dynamic response of NewFocus 1801 amplified photodetectors. The most essential requirements for error-free calibration of a fiber-optic pyrometer using a coiled irradiance standard lamp are discussed. All these conditions are validated in actual radiometric tests and shock temperature experiments on single-crystal NaCl and MgO. [Preview Abstract] |
Tuesday, June 16, 2015 4:15PM - 4:30PM |
L2.00003: Optical Properties of Lithium Fluoride under Extreme Stress and Strain-Rate Conditions P.A. Rigg, M.D. Knudson, R.J. Scharff, R.S. Hixson Lithium fluoride (LiF) is by far the most widely used window material in shock compression experiments due to many factors. These include material stability, availability in any reasonable size, and well-known shock properties. However, as with many transparent materials, the refractive index of LiF is density dependent. When used as an optical window in velocimetry experiments, this leads to the measurement of a velocity at the shocked sample/window interface that is incorrect. Therefore to calibrate LiF for use in these types of experiments, an independent set of experiments in which the particle velocity is known by means other than the velocimetry measurement must be done first. The results of an experimental study to determine this calibration to 200 GPa will be described and the accuracy of these results in comparison to past work will be discussed. [Preview Abstract] |
Tuesday, June 16, 2015 4:30PM - 4:45PM |
L2.00004: Transport properties of LiF under strong compression: modeling using advanced electronic structure methods and classical molecular dynamics Thomas R. Mattsson, Reese Jones, Donald Ward, Catalin Spataru, Luke Shulenburger, Lorin X. Benedict Window materials are ubiquitous in shock physics and with high energy density drivers capable of reaching multi-Mbar pressures the use of LiF is increasing. Velocimetry and temperature measurements of a sample through a window are both influenced by the assumed index of refraction and thermal conductivity, respectively. We report on calculations of index of refraction using the many-body theory GW and thermal ionic conductivity using linear response theory and model potentials. The results are expected to increase the accuracy of a broad range of high-pressure shock- and ramp compression experiments. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Tuesday, June 16, 2015 4:45PM - 5:00PM |
L2.00005: Phase Doppler Anemometry as an Ejecta Diagnostic David Bell, David Chapman When a shock wave is incident on a free surface, micron sized pieces of the material can be ejected from the surface. Phase Doppler Anemometry (PDA) is being developed to simultaneously measure the size and velocity of the individual shock induced ejecta particles. The measurements will provide an insight into ejecta phenomena. The results from experiments performed on the 13 mm bore light gas gun at the Institute of Shock Physics, Imperial College London are presented. Specially grooved tin targets were shocked at pressures of up to 14 GPa, below the melt on release pressure, to generate ejecta particles. The experiments are the first time that PDA has been successfully fielded on dynamic ejecta experiments. The results and the current state of the art of the technique are discussed along with the future improvements required to further improve performance and increase usability. [Preview Abstract] |
Tuesday, June 16, 2015 5:00PM - 5:15PM |
L2.00006: VISAR Unfold Analysis of MagLIF Laser Blast Wave Experiments Mark Hess, Kyle Peterson, Adam Harvey-Thompson MagLIF (Magnetized Liner Inertial Fusion) [1] is a fusion energy scheme, which utilizes a short laser pulse to preheat a fuel, and a magnetically driven cylindrical liner to compress the fuel to high energy density plasma conditions. Recently, a set of successful experiments have been performed to evaluate the effectiveness of our preheat process in MagLIF using the Z-Beamlet [2] laser at Sandia. The fuel is preheated in the liner, with no compression from the Z-machine, and a VISAR diagnostic was fielded on the outer surface of the liner to measure velocity of the liner due to the pressure of the laser blast wave on the inner surface of the liner. In support of this program, we developed a fast unfold method of the VISAR data using semi-analytical techniques/numerical methods. The method incorporates appropriate boundary conditions at both edges of the VISAR foil, realistic EOS tables, and an additional pressure pulse time-delay feature for accurately unfolding the time-dependent pressure from the VISAR data. Our fully automated method can produce high-quality unfolds of the laser blast wave in under a minute. [1] S.A. Slutz et al, Phys. Plasmas 17, 056303 (2010). [2] P. Rambo et al, Appl. Opt. 44, 2421 (2005). [Preview Abstract] |
Tuesday, June 16, 2015 5:15PM - 5:30PM |
L2.00007: Spectral Response of Multilayer Optical Structures to Dynamic Loading David Scripka, Garrett LeCroy, Gyuhyon Lee, Changyan Sun, Zhitao Kang, Christopher J. Summers, Naresh N. Thadhani Distributed Bragg Reflectors and optical microcavities are multilayer optical structures with spectral properties that are intrinsically sensitive to external perturbations. With nanometer to micrometer dimensions and near instantaneous optical response, these structures show significant potential as the basis for mesoscale time-resolved diagnostics that can be used to probe the dynamic behavior of mesoscale heterogeneous materials. In order to characterize the optical and mechanical behavior of the multilayer structures, a coupled computational-experimental study is underway. A mechanistic analysis of the spectral response of the structures to dynamic loading will be presented, along with computational simulations illustrating the observable spectral effects of 1D shock compression. Results from fabrication of specific multilayer designs and initial laser-driven shock loading experiments will be shown and compared to the simulation results. Preliminary results indicate that the magnitude of dynamic loading can be directly correlated to the altered spectral response. Potential applications of the theoretical diagnostics and challenges associated with spatially resolved data collection methodology will also be discussed. [Preview Abstract] |
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