CHEMEOS: a new chemical-picture-based model for plasma equation-of-state calculations

Conference · Thu Jan 01 04:00:00 EST 2004

DOI:https://doi.org/10.1063/1.1824870· OSTI ID:977687

Hakel, P ^[1]; Kilcrease, D P ^[2]

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1. Peter
2. David P.

We present the results of a new plasma equation-of-state (EOS) model currently under development at the Atomic and Optical Theory Group (T-4) in Los Alamos. This model is based on the chemical picture of the plasma and uses the free-energy-minimization technique and the occupation-probability formalism. The model is constructed as a combination of ideal and non-ideal contributions to the total Helmholtz free energy of the plasma including the effects of plasma microfields, strong coupling, and the hard-sphere description of the finite sizes of atomic species with bound electrons. These types of models have been recognized as a convenient and computationally inexpensive tool for modeling of local-thermal-equilibrium (LIE) plasmas for a broad range of temperatures and densities. We calculate the thermodynamic characteristics of the plasma (such as pressure and internal energy), and populations and occupation probabilities of atomic bound states. In addition to a smooth truncation of partition functions necessary for extracting ion populations from the system of Saha-type equations, the occupation probabilities can also be used for the merging of Rydberg line series into their associated bound-free edges. In the low-density, high-temperature regimes the plasma effects are adequately described by the Debye-Huckel model and its corresponding contribution to the total Helmholtz free energy of the plasma. In strongly-coupled plasmas, however, the Debye-Huckel approximation is no longer appropriate. In order to extend the validity of our EOS model to strongly-coupled plasmas while maintaining the analytic nature of our model, we adopt fits to the plasma free energy based on hypernetted-chain and Monte Carlo simulations. Our results for hydrogen are compared to other theoretical models. Hydrogen has been selected as a test-case on which improvements in EOS physics are benchmarked before analogous upgrades are included for any element in the EOS part of the new Los Alamos opacity code ATOMIC.

• Research Organization: Los Alamos National Laboratory
• Sponsoring Organization: DOE
• OSTI ID: 977687
• Report Number(s): LA-UR-04-4072
• Country of Publication: United States
• Language: English

Related Subjects

08 HYDROGEN
APPROXIMATIONS
BOUND STATE
ELECTRONS
FREE ENERGY
HYDROGEN
OCCUPATIONS
OPACITY
PARTITION FUNCTIONS
PHYSICS
PLASMA
SIMULATION
THERMODYNAMICS