Effects Of Line Shift On Plasma Radiative Opacity

As a simplified model, average-atom (AA) model has been applied widely in the practical engineering research of radiative opacity. Ions of different stages of a plasma in local thermodynamic equilibrium approximation (LTE) can be treated as an average ion with shell structure, the electrons distribute on each electron orbits, and the population can be non-integer. When plasma absorbs photons, electrons transit between different orbits. The electron orbital energy of the different ion-stages as well as different configurations is different in the hot plasmas, therefore the lines of same transition can distribute in certain energy range. The AA model, as one kind of statistical model, has brought certain statistical error. One is that the position of the transition energy is determined by the difference of average energy of the two relative electron orbits, thus comparing to the detailed model, the transition energy of AA model has a relative shift, which we called line shift.This paper present the radiative opacities of iron of the isothermal sequence of 20eV at the densities of 10^-2g/cm³, 10^-3g/cm³ and 10^-4g/cm³ using an average atom (AA) approach with modification of the transition energy. After the modification, the line positions of the transition 3s-3p had perfectly agreed with the results of the detailed term accounting (DTA) model, however differences still exist in the transition 3p-3d, to eliminate the differences the effect of the charge state distribution should be included in future studies. We can get the factors which influence the value of line shift. First is that whether the transition is between the same shells, second is the population of the initial transition shell, the last is that whether the transition is between the shells with same angular momentum. This paper also present the effects of line shift on the radiative opacities of bromine at temperature of 170eV and density of 10^-2g/cm³, and of sodium fluoride of the isodense sequence of 10^-2g/cm³ at the temperatures of 20eV, 40eV and 60eV and of iron at temperature of 200eV and density of 10^-2g/cm³. In these plasmas, the transitions of different inner shells have the main contributions to the total radiative opacity, but these line shifts are small, and these transition energies are high. Therefore, the line shifts can be ignored in the calculation of the radiative opacity.