Plasma Physics (physics.plasm-ph)

Abstract: We present novel first-principle fermionic path integral Monte Carlo (PIMC) simulation results for a dense partially ionized hydrogen (deuterium) plasma, for temperatures in the range $15,000$K $\leq T \leq 400,000$K and densities $7 \cdot 10^{-7}$g/cm$^{3}\leq \rho_H \leq 0.085$ g/cm$^{3}$ ($1.4 \cdot 10^{-6}$g/cm$^{3}\leq \rho_D \leq 0.17$ g/cm$^{3}$), corresponding to $100\geq r_s\geq 2$, where $r_s=\bar r/a_B$ is the ratio of the mean interparticle distance to the Bohr radius. These simulations are based on the fermionic propagator PIMC (FP-PIMC) approach in the grand canonical ensemble [A. Filinov \textit{et al.}, Contrib. Plasma Phys. \textbf{61}, e202100112 (2021)] and fully account for correlation and quantum degeneracy and spin effects. For the application to hydrogen and deuterium, we develop a combination of the fourth-order factorization and the pair product ansatz for the density matrix. Moreover, we avoid the fixed node approximation that may lead to uncontrolled errors in restricted PIMC (RPIMC). Our results allow us to critically re-evaluate the accuracy of the RPIMC simulations for hydrogen by Hu \textit{et al.} [Phys. Rev. B \textbf{84}, 224109 (2011)] and of various chemical models. The deviations are generally found to be small, but for the lowest temperature, $T=15,640$~K they reach several percent. We present detailed tables with our first principles results for the pressure and energy isotherms.

Abstract: Collective optical Thomson scattering (TS) is a diagnostic commonly used to characterize plasma parameters. These parameters are typically extracted by a fitting algorithm that minimizes the difference between a measured scattered spectrum and an analytic spectrum calculated from the velocity distribution function (VDF) of the plasma. However, most existing TS analysis algorithms assume the VDFs are Maxwellian, and applying an algorithm which makes this assumption does not accurately extract the plasma parameters of a non-Maxwellian plasma due to the effect of non-Maxwellian deviations on the TS spectra. We present new open-source numerical tools for forward modeling analytic spectra from arbitrary VDFs, and show that these tools are able to more accurately extract plasma parameters from synthetic TS spectra generated by non-Maxwellian VDFs compared to standard TS algorithms. Estimated posterior probability distributions of fits to synthetic spectra for a variety of example non-Maxwellian VDFs are used to determine uncertainties in the extracted plasma parameters, and show that correlations between parameters can significantly affect the accuracy of fits in plasmas with non-Maxwellian VDFs.