Contribution of electron-atom collisions to the plasma conductivity of noble gases

Transport properties of warm dense neon and krypton at high pressures

The transport properties of warm dense neon (Ne) and krypton (Kr) are studied by combining self-consistent fluid variational theory (SFVT) with linear response theory (LRT). The components are determined using the SFVT, and the transport parameters, including the electrical conductivity, thermal conductivity, and thermopower, are calculated with the LRT. The relevant scattering mechanisms, including electron-ion, electron-electron, and electron-atom scatterings, are taken into account. An effective potential model in combination with the Muffin-tin model is introduced to further improve the description for electron-atom scattering, which not only includes static, exchange, and polarization interactions but also considers the plasma environmental effects. It is found that for electron-atom scattering, the influence of the plasma density is significant at lower scattering energies but the effects are different for electron-Ne and electron-Kr scattering. For electron-Kr scattering, a plasma density-dependent Ramsauer-Townsend minimum is observed. The obtained transport parameters are compared with the available experiments and other simulations. The plasma phase transition of warm dense Kr is revisited from multiple perspectives based on the numerical simulation results for the electrical conductivity and thermopower. These observations may help one to better understand the transport properties of warm dense noble gases and are an important guide for future experimental designs and theoretical developments.

Model of electron transport in dense plasmas spanning temperature regimes

We present a new model of electron transport in warm and hot dense plasmas which combines the quantum Landau-Fokker-Planck equation with the concept of mean-force scattering. We obtain electrical and thermal conductivities across several orders of magnitude in temperature, from warm dense matter conditions to hot, nondegenerate plasma conditions, including the challenging crossover regime between the two. The small-angle approximation characteristic of Fokker-Planck collision theories is mitigated to good effect by the construction of accurate effective Coulomb logarithms based on mean-force scattering, which allows the theory to remain accurate even at low temperatures, as compared with high-fidelity quantum simulation results. Electron-electron collisions are treated on equal footing as electron-ion collisions. Their accurate treatment is found to be essential for hydrogen, and is expected to be important to other low-Z elements. We find that electron-electron scattering remains influential to the value of the thermal conductivity down to temperatures somewhat below the Fermi energy. The accuracy of the theory seems to falter only for the behavior of the thermal conductivity at very low temperatures due to a subtle interplay between the Pauli exclusion principle and the small-angle approximation as they pertain to electron-electron scattering. Even there, the model is in fair agreement with ab initio simulations.

Polarized angular-dependent reflectivity and density-dependent profiles of shock-compressed xenon plasmas

New data for the reflectivity of shock-compressed xenon plasmas at pressures of 10-12 GPa at large incident angles are presented. In addition, measurements have been performed at different densities. These data allow to analyze the free-electron density profile across the shock wave front. Assuming a Fermi-like density profile, the width of the front layer is inferred. The reflectivity coefficients for the s- and p-polarized waves are calculated. The influence of atoms, which was taken into account on the level of the collision frequency, proves to be essential for the understanding of the reflection process. Subsequently, a unique density profile is sufficient to obtain good agreement with the experimental data at different incident angles and at all investigated optical laser frequencies. Reflectivity measurements for different densities allow to determine the dependence of shock-front density profiles on the plasma parameters. As a result, it was found that the width of the front layer increases with decreasing density.