Stark-Broadening of Ar K-Shell Lines: A Comparison between Molecular Dynamics Simulations and MERL Results

• Main Authors: Marco A. Gigosos, Roberto C. Mancini, Juan M. Martín-González, Ricardo Florido
• Format: Article
• Language: English
• Published: MDPI AG 2021-01-01
• Series: Atoms
• Subjects: stark broadening; electron broadening; recombination broadening; simulations; molecular dynamics
• Online Access: https://www.mdpi.com/2218-2004/9/1/9

Analysis of Stark-broadened spectral line profiles is a powerful, non-intrusive diagnostic technique to extract the electron density of high-energy-density plasmas. The increasing number of applications and availability of spectroscopic measurements have stimulated new research on line broadening theory calculations and computer simulations, and their comparison. Here, we discuss a comparative study of Stark-broadened line shapes calculated with computer simulations using non-interacting and interacting particles, and with the multi-electron radiator line shape MERL code. In particular, we focus on Ar K-shell X-ray line transitions in He- and H-like ions, i.e., He<inline-formula><math display="inline"><semantics><msub><mrow></mrow><mi>α</mi></msub></semantics></math></inline-formula>, He<inline-formula><math display="inline"><semantics><msub><mrow></mrow><mi>β</mi></msub></semantics></math></inline-formula> and He<inline-formula><math display="inline"><semantics><msub><mrow></mrow><mi>γ</mi></msub></semantics></math></inline-formula> in He-like Ar and Ly<inline-formula><math display="inline"><semantics><msub><mrow></mrow><mi>α</mi></msub></semantics></math></inline-formula>, Ly<inline-formula><math display="inline"><semantics><msub><mrow></mrow><mi>β</mi></msub></semantics></math></inline-formula> and Ly<inline-formula><math display="inline"><semantics><msub><mrow></mrow><mi>γ</mi></msub></semantics></math></inline-formula> in H-like Ar. These lines have been extensively used for X-ray spectroscopy of Ar-doped implosion cores in indirect- and direct-drive inertial confinement fusion (ICF) experiments. The calculations were done for electron densities ranging from <inline-formula><math display="inline"><semantics><msup><mn>10</mn><mn>23</mn></msup></semantics></math></inline-formula> to <inline-formula><math display="inline"><semantics><mrow><mn>3</mn><mo>×</mo><msup><mn>10</mn><mn>24</mn></msup></mrow></semantics></math></inline-formula> cm<inline-formula><math display="inline"><semantics><msup><mrow></mrow><mrow><mo>−</mo><mn>3</mn></mrow></msup></semantics></math></inline-formula> and a representative electron temperature of 1 keV. Comparisons of electron broadening only and complete line profiles including electron and ion broadening effects, as well as Doppler, are presented. Overall, MERL line shapes are narrower than those from independent and interacting particles computer simulations performed at the same conditions. Differences come from the distinctive treatments of electron broadening and are more pronounced in <inline-formula><math display="inline"><semantics><mi>α</mi></semantics></math></inline-formula> line transitions. We also discuss the recombination broadening mechanism that naturally emerges from molecular dynamics simulations and its influence on the line shapes. Furthermore, we assess the impact of employing either molecular dynamics or MERL line profiles on the diagnosis of core conditions in implosion experiments performed on the OMEGA laser facility.