Model uncertainties of local-thermodynamic-equilibrium K-shell spectroscopy

T. Nagayama (a) , J.E. Bailey (a), R.C. Mancini (b), C.A. Iglesias (c), S.B. Hansen (a), C. Blancard (d), H.K. Chung (e), J. Colgan (f), Ph. Cosse (d), G. Faussurier (d), R. Florido (g), C.J. Fontes (f), F. Gilleron (d), I.E. Golovkin (h), D.P. Kilcrease (f), G. Loisel (a), J.J. MacFarlane (h), J.-C. Pain (d), G.A. Rochau (a), M.E. Sherrill (f), R.W. Lee (i)

(a) Sandia National Laboratories, Albuquerque, NM 87185, USA. (b) University of Nevada, Reno, NV 89557, USA. (c) Lawrence Livermore National Laboratory, Livermore, CA 94550, USA. (d) Commissarat à I’Énergie Atomique (CEA) et aux Énergies Alternatives, F-91297 Arpajon, France. (e)  International Atomic Energy Agency, A-1400 Vienna, Austria. (f) Los Alamos National Laboratory, Los Alamos, NM, 87545, USA. (g) Departamento de Física, Universidad de Las Palmas de Gran Canaria, 35017 Las Palmas de Gran Canaria, Spain. (h) Prism Computational Sciences, Madison, WI 53703, USA. (i) Institute for Material Dynamics at Extreme Conditions, University of California, Berkeley, CA, 94720, USA.

Local-thermodynamic-equilibrium (LTE) K-shell spectroscopy is a common tool to diagnose electron density, ne, and electron temperature, Te, of high-energy-density (HED) plasmas. Knowing the accuracy of such diagnostics is important to provide quantitative conclusions of many HED-plasma research efforts. For example, Fe opacities were recently measured at multiple conditions at the Sandia National Laboratories Z machine (Bailey et al., 2015), showing significant disagreement with modeled opacities. Since the plasma conditions were measured using K-shell spectroscopy of tracer Mg (Nagayama et al., 2014), one concern is the accuracy of the inferred Fe conditions. In this article, we investigate the K-shell spectroscopy model uncertainties by analyzing the Mg spectra computed with 11 different models at the same conditions. We find that the inferred conditions differ by ±20–30% in ne and ±2–4% in Te depending on the choice of spectral model. Also, we find that half of the Te uncertainty comes from ne uncertainty. To refine the accuracy of the K-shell spectroscopy, it is important to scrutinize and experimentally validate line-shape theory. We investigate the impact of the inferred ne and Te model uncertainty on the Fe opacity measurements. Its impact is small and does not explain the reported discrepancies.

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