Improved Enthalpy-based Equation of State and application to Solid and Porous Lithium Deuteride

The main aim of this paper is to describe the improvements to the enthalpy-based equation of state, and results of application to solid as well as porous lithium deuteride. In addition to being the lightest compound (which is an insulator at normal conditions), this material is an important component in devices employing thermonuclear fusion. The enthalpy-parameter versus pressure variation on five curves are used to provide an interpolation formula for its dependence on temperature. Then, a refined treatment of pore collapse, based on the $P-\alpha$ model and Menikoff's modification, is incorporated in the formalism, and checked with data on compaction of Cu powder. The enthalpy-based equation of state is applied to compute the Hugoniot of natural lithium deuteride (up to $10^3$ GPa pressure) and lithium-6 deuteride (up to $10^{6}$ GPa pressure). Comparison of predictions of the method with available data also includes porous cases up to initial density ratio of 1.78. The implementation of the equation of state in a hydrodynamic simulation code, which uses the flux-corrected-transport algorithm, is also briefly discussed. Simulation results for pressure versus fluid-velocity data show excellent agreement with those from Hugoniot experiments. Brief accounts of Vinet's zero-temperature isotherm, extended with that of the quantum statistical model, and the ion equation of state, which includes Debye-Einstein model, melting, rotation and vibration contributions of the molecule, and its dissociation are provided. Also, excellent new approximations to the electron equation of state contributions, based on Thomas-Fermi model are also discussed.