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Cochrane, Kyle

Publications and source records attributed to Cochrane, Kyle.

At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Shock compression of strongly correlated oxides: A liquid-regime equation of state for cerium(IV) oxide

Here, the shock Hugoniot for full-density and porous CeO 2 was investigated in the liquid regime using ab initio molecular dynamics (AIMD) simulations with Erpenbeck's approach based on the Rankine-Hugoniot jump conditions. The phase space was sampled by carrying out NVT simulations for isotherms between 6000 and 100 000 K and densities ranging from ρ = 2.5 to 20 g/cm 3 . The impact of on-site Coulomb interaction corrections +U on the equation of state (EOS) obtained from AIMD simulations was assessed by direct comparison with results from standard density functional theory simulations. Classical molecular dynamics (CMD) simulations were also performed to model atomic-scale shock compression of larger porous CeO 2 models. Results from AIMD and CMD compression simulations compare favorably with Z-machine shock data to 525 GPa and gas-gun data to 109 GPa for porous CeO 2 samples. Using results from AIMD simulations, an accurate liquid-regime Mie-Grüneisen EOS was built for CeO 2 . In addition, a revised multiphase SESAME-type EOS was constrained using AIMD results and experimental data generated in this work. This study demonstrates the necessity of acquiring data in the porous regime to increase the reliability of existing analytical EOS models.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

Exploring magnetized liner inertial fusion with a semi-analytic model

In this paper, we explore magnetized liner inertial fusion (MagLIF) [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)] using a semi-analytic model [R. D. McBride and S. A. Slutz, Phys. Plasmas 22, 052708 (2015)]. Specifically, we present simulation results from this model that: (a) illustrate the parameter space, energetics, and overall system efficiencies of MagLIF; (b) demonstrate the dependence of radiative loss rates on the radial fraction of the fuel that is preheated; (c) explore some of the recent experimental results of the MagLIF program at Sandia National Laboratories [M. R. Gomez et al., Phys. Rev. Lett. 113, 155003 (2014)]; (d) highlight the experimental challenges presently facing the MagLIF program; and (e) demonstrate how increases to the preheat energy, fuel density, axial magnetic field, and drive current could affect future MagLIF performance.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Shock compression response of poly(4-methyl-1-pentene) plastic to 985 GPa

Poly(4-methyl-1-pentene) plastic (PMP) is a hydrocarbon polymer with potential applications to inertial confinement fusion experiments and as a Hugoniot impedance matching standard for equation of state experiments. Using Sandia's Z-machine, we performed a series of flyer plate experiments to measure the principal Hugoniot and reshock states of PMP up to 985 GPa. The principal Hugoniot measurements validate density functional theory (DFT) calculations along the Hugoniot. The DFT calculations are further analyzed using a bond tracking method to understand the dissociation pathway under shock compression. Complete dissociation occurs at a compression factor similar to other sp3-hybridized, C-C bonded systems, which suggests a limiting compression for C-C bonds. The combined experimental and DFT results provide a solid basis for constructing an equation of state model for PMP.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Calculating the dissociation chemistry and equation of state properties of materials [Slides]

Many experimental techniques are accurate enough to reveal glaring weaknesses in the material models used by physics codes to design them. This is requiring ever more stringent equation of state (EOS) development. Formerly, EOS models were built using limited gas gun shock data and a few general physics assumptions. With the ever increasing computer power available, we began using density functional theory (DFT) to approximate other EOS regimes such as the principal isentrope, critical point, and sometimes melt. With Sequoia, and only because of Sequoia’s capacity, we are now calculating a limited range, general EOS table and then deriving the above EOS properties based on that table, often on a shorter time frame and more thoroughly than we used to compute just the EOS sections listed above. The first project was to calculate a limited range EOS for CO 2 and specifically track the dissociated species present at each density and temperature. We would not see all of the possible species due to our small sample size and limited time, however, we should see the dominant species and general trends. This work was done to support a new, chemistry aware EOS model that is still under development at LANL. The second project was done for two reasons. The first is LANL and SNL are developing a new amorphous SiO 2 EOS for use in hydrocodes. There is extensive principal Hugoniot and isentrope data, but very little lower density data. There is also no real estimate of the critical point so we found the approximate value of that as well. The second reason for lower density SiO 2 is to test a new method for calculating the Hugoniot of porous materials. Because aerogel (low density SiO 2 ) is used extensively in many shock experiments, there was a large data set to compare with. As can be seen in the figure, the new method appears to work well and is tracking the porous Hugoniot within the experimental error bars (not shown). Finally, SNL is developing a new EOS for LiF because we were seeing discrepancies with the SESAME table. DFT has some issues calculating EOS values for LiF, so we will make some corrections, however, our first attempt appears to have very good results which confirm several experimentally seen properties, as seen on the previous slide.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗