Fengtao Jin

Influence of the electronic energy level broadening on the ionization of atoms in hot and dense plasmas: An average atom model demonstration

The broadening of the electronic energy levels of atoms and ions in hot and dense plasmas is taken to be an energy band with a Gaussian distribution of the density of states, which is normalized to ensure that the integration of the density of state over one band is equal to the statistical weight of the corresponding atomic level. The distribution of the bound electrons among the energy bands is determined by the continuum Fermi-Dirac distribution. Within a self-consistent field average atom approach, it has been shown that explicit considerations for the electronic energy level broadening have significant effects on the ionization of the atoms in hot and dense plasmas. The instability of the pressure induced electronic ionization with density, which occurs often in a normal average atom model and is avoided usually by introducing pseudoshape resonance states, disappears naturally. As examples, the density dependence of the average ionization of Al and Au at 1, 10, 100, and 1000 eV are presented.

Population kinetics and M band emission spectra of gold plasmas in non-local thermodynamic equilibrium by using a detailed relativistic configuration approach

A collisional-radiative model based on the approach of detailed relativistic configurations is developed, where the complete set of atomic data including photo-excitation, photoionization, electron impact excitation, electron impact ionization and autoionization is calculated, and the data of the inverse processes are obtained by detailed balance. The population distribution is obtained by solving the rate equation under the steady-state condition. The present model is applied to calculate the charge state distribution and M band emission spectra of gold plasmas in non-local thermodynamic equilibrium under a variety of plasma conditions. Comparisons between the present work and experimental results were made and good agreement is found. For the strong transition lines, the intensities predicted by the present model agree with those of experimental spectra within 50%. The present work is useful in analyzing and interpreting experiments as well as in diagnosing the electron temperature in experiments.

RADIATIVE OPACITY OF IRON STUDIED USING A DETAILED LEVEL ACCOUNTING MODEL

The opacity of iron plasma in local thermodynamic equilibrium is studied using an independently developed detailed level accounting model. Atomic data are generated by solving the full relativistic Dirac-Fock equations. State mixing within one electronic configuration is considered to include part of the correlations between electrons without configuration interaction matrices that are too large being involved. Simulations are carried out and compared with several recent experimental transmission spectra in the M- and L-shell absorption regions to reveal the high accuracy of the model. The present model is also compared with the OPAL, LEDCOP and OP models for two isothermal series at T = 20 eV and T = 19.3 eV. It is found that our model is in good agreement with OPAL and LEDCOP while it has discrepancies with OP at high densities. Systematic Rosseland and Planck mean opacities in the range 10-1000 eV for temperature and 10–5-10–1 g cm–3 for density are also presented and compared with LEDCOP results, finding good agreement at lower temperatures but apparent differences at high temperatures where the L- and K-shell absorptions are dominant.

The influence of core–valence electron correlations on the convergence of energy levels and oscillator strengths of ions with an open 3d shell using Fe VIII as an example

Accurate atomic data, such as fine structure energy levels and oscillator strengths of different ionization stages of iron ions, are important for astrophysical and laboratory plasmas. However, some important existing oscillator strengths for ions with an open 3d shell found in the literature might not be accurate enough for practical applications. As an example, the present paper checks the convergence behaviour of the energy levels and oscillator strengths of Fe VIII by systematically increasing the 3pn–3dn (n = 1, 2, 3 and 6) core–valence electron correlations using the multiconfiguration Hartree–Fock method. The results show that one should at least include up to 3p3–3d3 core–valence electron correlations to obtain converged results. Large differences are found between the present oscillator strengths and other theoretical results in the literature for some strong transitions.

A detailed simulation for the transmission spectrum of hot aluminium plasma

The experimental transmission spectrum [Jiamin Yang et al., Phys. Plasmas 10, 4881 (2003)] of hot aluminium plasma is simulated by using a detailed term accounting model. The fine absorption structures are reproduced reasonably well for both the absorption strength and the line positions. The discrepancies between the detailed simulation and the experiment show that the temperature gradient exists in the experimental sample. By fitting the measured transmission spectrum with the variation of the population of the ion stage, it is concluded that the experimental transmission spectrum was obtained mainly at the temperature of about 65 eV but overlapped by some lower temperature spectra of even down to 35 eV. The relative strength of the fine absorption lines within one stage of the ion cannot be reproduced accurately without considering the non-Boltzmann distributions among the energy levels of the ion.

Energy level broadening effect on the equation of state of hot dense Al and Au plasma

In the hot dense matter regime, the isothermal equation of state (EOS) of Al and Au is calculated using an average-atom (AA) model in which the broadening of energy levels of atoms and ions are accounted for by using with a Gaussian distribution of the density of states. The distribution of bound electrons in the energy bands is determined by the continuum Fermi–Dirac distribution. With a self-consistent field average atoms scheme, it is shown that the energy-level broadening has a significant effect on the isothermal equation of state (EOS) of Al and Au in the hot dense matter regime. The jumps in the equation of state (EOS) induced by pressure ionization of the one-electron orbital with the increase in density, which often occur in the normal average-atom model and have been avoided by generally introducing the pseudo-shape resonance states, disappear naturally.

Multi-charge-state molecular dynamics and self-diffusion coefficient in the warm dense matter regime

We present a multi-ion molecular dynamics (MIMD) simulation and apply it to calculating the self-diffusion coefficients of ions with different charge-states in the warm dense matter (WDM) regime. First, the method is used for the self-consistent calculation of electron structures of different charge-state ions in the ion sphere, with the ion-sphere radii being determined by the plasma density and the ion charges. The ionic fraction is then obtained by solving the Saha equation, taking account of interactions among different charge-state ions in the system, and ion–ion pair potentials are computed using the modified Gordon–Kim method in the framework of temperature-dependent density functional theory on the basis of the electron structures. Finally, MIMD is used to calculate ionic self-diffusion coefficients from the velocity correlation function according to the Green–Kubo relation. A comparison with the results of the average-atom model shows that different statistical processes will influence the ionic ...

Effects of an ambient radiation field on charge state distribution of NLTE carbon plasmas

A collisional-radiative model based on detailed level approach is developed to investigate the population kinetics of non-local thermodynamic equilibrium (NLTE) carbon plasmas. Present model is used to diagnose a recent measurement for average ionization degree of carbon plasmas at 0.2 g/cm3 [G. Gregori et al., Phys. Rev. Lett. 101, 045003 (2008)]. Physical factors which may influence the population kinetics are investigated in detail and it indicates that the high temperature radiative field plays an important role on the ionization balance.

Progress of opacity experiment on the Shengguang II Laser Facility

In recent years, a series of opacity diagnostics have been developed at the Research Center of Laser Fusion in China. Two types of cavities (a conical cavity called a type I target, and a cylindrical cavity with foam baffles called a type II target) were designed to convert the eight-beam laser into x-ray radiation to efficiently heat the sample and to prevent the sample from irradiation of the reflected laser and plasmas on the Shengguang II laser facility. Typical opacity experiments have been carried out using the two target designs, respectively. The results show that a sample temperature of about 95 eV has been reached using the type II target which is the highest obtained on the high power laser facility.