Detailed computation of hot-plasma atomic spectra

TL;DR

This paper discusses advancements in the SCO-RCG opacity code, including models for complex transition arrays, magnetic field effects, and efficient line profile calculations, improving accuracy in hot plasma spectral analysis.

Contribution

The paper introduces the Partially-Resolved-Transition-Array model and a fast algorithm for line profile convolution, enhancing spectral modeling in hot plasma research.

Findings

Improved modeling of transition arrays with the Partially-Resolved-Transition-Array.

Efficient convolution algorithm for Zeeman line profiles using cubic splines.

Enhanced accuracy in opacity and emissivity calculations under magnetic fields.

Abstract

We present recent evolutions of the detailed opacity code SCO-RCG which combines statistical modelings of levels and lines with fine-structure calculations. The code now includes the Partially-Resolved-Transition-Array model, which allows one to replace a complex transition array by a small-scale detailed calculation preserving energy and variance of the genuine transition array and yielding improved high-order moments. An approximate method for studying the impact of strong magnetic field on opacity and emissivity was also recently implemented. The Zeeman line profile is modeled by fourth-order Gram-Charlier expansion series, which is a Gaussian multiplied by a linear combination of Hermite polynomials. Electron collisional line broadening is often modeled by a Lorentzian function and one has to calculate the convolution of a Lorentzian with Gram-Charlier distribution for a huge number of spectral lines. Since the numerical cost of the direct convolution would be prohibitive, we propose, in order to obtain the resulting profile, a fast and precise algorithm, relying on a representation of the Gaussian by cubic splines.