Ammonia and water are critical components of extraterrestrial bodies, determining the density and physical properties of the Outer Planets, their moons, and of extrasolar planets. Ammonia is unusual in having a high heat capacity relative to other molecular species. Equations of state (EOS) are presented for ammonia and for mixtures of ammonia and water. Their properties are discussed in terms of chemical compositions that evolve as pressure and temperature are varied. The NH4OH hydrate of ammonia is known to exist as a separate molecular species at pressures above about 5 GPa, and an effort was made to include reaction between NH3 and H2O in the mixture EOS. The EOS are suitable for calculating structures of icy planets and exoplanets, and of impacts. mass-radius relations which bound the possible interpretations of composition and structure for extraterrestrial bodies of unknown composition, such as exoplanets.

Ratchet growth, or irreversible thermal expansion of the TATB-based plastic-bonded explosive PBX-9502, leads to increased sensitivity, as a result of increased porosity. The observed increase of between 3.1 and 3.5 volume percent should increase sensitivity according to the published Pop-plots for PBX-9502 [1]. Because of the variable size, shape, and location of the increased porosity, the observed sensitivity of the ratchet-grown sample is less than the sensitivity of a sample pressed to the same density. Modeling of the composite, using a quasi-harmonic EOS for unreacted components [2] and a robust porosity model for variations in density [3], allowed comparison of the initiation observed in experiment with behavior modeled as a function of density. An Arrhenius model was used to describe reaction, and the EOS for products was generated using the CHEETAH code [4]. A 1-D Lagrangian hydrocode was used to model in-material gauge records and the measured turnover to detonation, predicting greater sensitivity to density than observed for ratchet-grown material. This observation is consistent with gauge records indicating intermittent growth of the reactive wave, possibly due to inhomogeneities in density, as observed in SEM images of the material [5].

An accurate EOS for polystyrene foam is necessary for analysis of numerous experiments in shock compression, inertial confinement fusion, and astrophysics. Plastic to gas ratios vary between various samples of foam, according to the density and cell-size of the foam. A matrix of compositions has been investigated, allowing prediction of foam response as a function of the plastic-to-air ratio. The EOS code CHEETAH allows participation of the air in the decomposition reaction of the foam. Differences between air-filled, Ar-blown, and CO2-blown foams are investigated, to estimate the importance of allowing air to react with products of polystyrene decomposition. O-2-blown foams are included in some comparisons, to amplify any consequences of reaction with oxygen in air. He-blown foams are included in some comparisons, to provide an extremum of density. Product pressures are slightly higher for oxygen-containing fill gases than for non-oxygen-containing fill gases. Examination of product species indicates that CO2 decomposes at high temperatures.

The plastic response of beryllium was investigated during loading by laser-induced shock waves, using surface velocimetry and in-situ x-ray diffraction. Results from loading by thermal x-rays (hohlraum) were consistent with more extensive studies using laser ablation. Strong elastic waves were observed, up to ~1 km/s in free surface speed, with significant structure before the arrival of the plastic shock. The magnitude and shape of the precursor could be reproduced with a plasticity model based on dislocation dynamics. Changes in lattice spacing measured from the x-ray diffraction pattern gave a direct measurement of uniaxial compression in the elastic wave, triaxial flow from the decay of the precursor, and triaxial compression in the plastic shock; these were consistent with the velocity data. The dynamic strength behavior deduced from the laser experiments was used to help interpret surface velocity data around the onset of shock-induced melting. A model of heterogeneous mixtures is being extended to treat anisotropic components, and spall.

The plastic response of beryllium was investigated during loading by laser-induced shock waves, using surface velocimetry and in-situ x-ray diffraction. Results from loading by thermal x-rays (hohlraum) were consistent with more extensive studies using laser ablation. Strong elastic waves were observed, up to ~1 km/s in free surface speed, with significant structure before the arrival of the plastic shock. The magnitude and shape of the precursor could be reproduced with a plasticity model based on dislocation dynamics. Changes in lattice spacing measured from the x-ray diffraction pattern gave a direct measurement of uniaxial compression in the elastic wave, triaxial flow from the decay of the precursor, and triaxial compression in the plastic shock; these were consistent with the velocity data. The dynamic strength behavior deduced from the laser experiments was used to help interpret surface velocity data around the onset of shock-induced melting. A model of heterogeneous mixtures is being extended to treat anisotropic components, and spall.

Modelling of off-Hugoniot states in an expanding interface subjected to a shock reveals the importance of a chemically complete description of the materials. Hydrodynamic experiments typically rely on pre-shot target characterization to predict how initial perturbations will affect the late-time hydrodynamic mixing. However, it is the condition of these perturbations at the time of shock arrival that dominates their eventual late-time evolution. In some cases these perturbations are heated prior to the arrival of the main shock. Correctly modelling how temperature and density gradients will develop in the pre-heated material requires an understanding of the equation-of-state. In the experiment modelled, an epoxy/foam layered package was subjected to tin L-shell radiation, producing an expanding assembly at a well-defined temperature. This assembly was then subjected to a controlled shock, and the evolution of the epoxy-foam interface imaged with x-ray radiography. Modelling of the data with the hydrodynamics code RAGE was unsuccessful under certain shock conditions, unless condensation of chemical species from the plasma is explicitly included. The EOS code Cheetah was used to prepare suitable EOS for input into the hydrodynamics modelling.

Submitted for the DPP07 Meeting of The American Physical Society Observation of Recurring Phase-Inversions in Radiatively Heated Single-Mode Sinusoidal Perturbations N.E. LANIER, J. WORKMAN, S.D. CROCKETT, R.L. HOLMES, R.N. MULFORD, B. PATTERSON, D. SCHMIDT, D. SWIFT, Los Alamos National Laboratory, P. GRAHAM, A. MOORE, Atomic Weapons Establishment — Experiments studying the hydrodynamic evolution of radiatively heated single-mode perturbations have been conducted at the OMEGA laser facility. An epoxy layer with a sinusoidal interface is embedded in foam and heated with tin L-shell radiation. As the epoxy expands, an optional shock, with independently controlled strength and timing, is introduced. The resulting hydrodynamic behavior is radiographically. Experimental data along with three-dimensional RAGE simulations are used to generate a more complete picture of this preheatinduced evolution. When preheated, the initial expansion of the sinusoidal perturbation forms a complex set of shocks and an interface that quickly becomes nonlinear. The interaction of these preheat-induced shocks result in density gradients, whose phase, with respect to the initial perturbation, oscillates in time. In this experiment, when the shock propagates through the evolving layer, these density gradients are the dominant influence on post-shock hydrodynamic behavior. This work is sponsored by U. S. DOE under Contract No. DE-AC52-06NA25396. Nicholas Lanier Los Alamos National Laboratory Date submitted: 17 Sep 2007 Electronic form version 1.4