R-Matrix calculations for opacities: I. Methodology and computations

TL;DR

This paper introduces an advanced R-matrix methodology for calculating plasma opacities, improving accuracy and resolving issues in existing models, with significant implications for astrophysics and high-temperature plasma research.

Contribution

It presents a comprehensive extension of the R-matrix method, including large-scale calculations and plasma broadening effects, to enhance opacity computations over traditional approaches.

Findings

R-matrix spectra differ from OP, leading to higher opacities.

Enhanced Rosseland and Planck mean opacities observed.

Revisions needed for heavy element opacities in high-temperature plasmas.

Abstract

An extended version of the R-matrix methodology is presented for calculation of radiative parameters for improved plasma opacities. Contrast and comparisons with existing methods primarily relying on the Distorted Wave (DW) approximation are discussed to verify accuracy and resolve outstanding issues, particularly with reference to the Opacity Project (OP). Among the improvements incorporated are: (i) large-scale Breit-Pauli R-matrix (BPRM) calculations for complex atomic systems including fine structure, (ii) convergent close coupling wave function expansions for the (e+ion) system to compute oscillator strengths and photoionization cross sections, (iii) open and closed shell iron ions of interest in astrophysics and experiments, (iv) a treatment for plasma broadening of autoionizing resonances as function of energy-temperature-density dependent cross sections, (v) a "top-up" procedure to compare convergence with R-matrix calculations for highly excited levels, and (vi) spectroscopic identification of resonances and bound \eion levels. The present R-matrix monochromatic opacity spectra are fundamentally different from OP and lead to enhanced Rosseland and Planck mean opacities. An outline of the work reported in other papers in this series and those in progress is presented. Based on the present re-examination of the OP work, it is evident that opacities of heavy elements require revisions in high temperature-density plasma sources.