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Title: Breakdown of the quasistatic approximation at high densities and its effect on the heliumlike K{alpha} complex of nickel, iron, and calcium

Abstract

Recent work to include R-matrix data within a larger model comprised mostly of distorted-wave and plane-wave Born data has resulted in the general spectral modeling (GSM) code. It employs a quasistatic approximation, a standard, low-density methodology that assumes the ionization balance is separable from a determination of the excited-state populations that give rise to the spectra. GSM further allows for some states to be treated statistically as contributions to effective rates, instead of being included explicitly in the kinetics model. While these two approximations are known to be valid at low densities, this work investigates using such methods to model high-density, non-LTE emission spectra and determines at what point the approximations break down by comparing to spectra produced by the Los Alamos National Laboratory code ATOMIC which makes no such approximations. As both approximations are used by other astrophysical and low-density modeling codes, the results should be of broad interest. He-like K{alpha} emission spectra are presented for three elements, Ni, Fe, and Ca, in order to gauge the effect of both the statistical methods and the ground-state-only, quasistatic approximation employed in GSM. This work confirms that at and above the temperature of maximum abundance of the He-like ionization stage, themore » range of validity for both approximations is sufficient for modeling the low- and moderate-density regimes one typically finds in astrophysical and magnetically confined fusion plasmas. However, a breakdown does occur for sufficiently high densities; we obtain quantitative limits that are significantly higher than previous works. Additionally, this work demonstrates that, while the range of validity for both approximations is sufficient to accurately predict the density-dependent quenching of the z line, the approximations begin to break down at higher densities. Thus, these approximations should be used with greater care when modeling high-density plasmas such as those found in laser-driven inertial confinement fusion and electromagnetic pinch devices.« less

Authors:
; ; ;  [1]
  1. Applied Physics Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
Publication Date:
OSTI Identifier:
21140643
Resource Type:
Journal Article
Journal Name:
Physical Review. A
Additional Journal Information:
Journal Volume: 76; Journal Issue: 6; Other Information: DOI: 10.1103/PhysRevA.76.062504; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1050-2947
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; APPROXIMATIONS; CALCIUM; CALCIUM IONS; DISTORTED WAVE THEORY; EMISSION SPECTRA; EXCITED STATES; GROUND STATES; INERTIAL CONFINEMENT; IONIZATION; IRON; LASER RADIATION; LTE; NICKEL; PINCH DEVICES; PLASMA; PLASMA DENSITY; QUENCHING; R MATRIX; SIMULATION; WAVE PROPAGATION

Citation Formats

Oelgoetz, Justin, Fontes, Christopher J, Honglin, Zhang, Pradhan, Anil K, and Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, Ohio 43210. Breakdown of the quasistatic approximation at high densities and its effect on the heliumlike K{alpha} complex of nickel, iron, and calcium. United States: N. p., 2007. Web. doi:10.1103/PHYSREVA.76.062504.
Oelgoetz, Justin, Fontes, Christopher J, Honglin, Zhang, Pradhan, Anil K, & Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, Ohio 43210. Breakdown of the quasistatic approximation at high densities and its effect on the heliumlike K{alpha} complex of nickel, iron, and calcium. United States. https://doi.org/10.1103/PHYSREVA.76.062504
Oelgoetz, Justin, Fontes, Christopher J, Honglin, Zhang, Pradhan, Anil K, and Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, Ohio 43210. 2007. "Breakdown of the quasistatic approximation at high densities and its effect on the heliumlike K{alpha} complex of nickel, iron, and calcium". United States. https://doi.org/10.1103/PHYSREVA.76.062504.
@article{osti_21140643,
title = {Breakdown of the quasistatic approximation at high densities and its effect on the heliumlike K{alpha} complex of nickel, iron, and calcium},
author = {Oelgoetz, Justin and Fontes, Christopher J and Honglin, Zhang and Pradhan, Anil K and Department of Astronomy, Ohio State University, 140 West 18th Avenue, Columbus, Ohio 43210},
abstractNote = {Recent work to include R-matrix data within a larger model comprised mostly of distorted-wave and plane-wave Born data has resulted in the general spectral modeling (GSM) code. It employs a quasistatic approximation, a standard, low-density methodology that assumes the ionization balance is separable from a determination of the excited-state populations that give rise to the spectra. GSM further allows for some states to be treated statistically as contributions to effective rates, instead of being included explicitly in the kinetics model. While these two approximations are known to be valid at low densities, this work investigates using such methods to model high-density, non-LTE emission spectra and determines at what point the approximations break down by comparing to spectra produced by the Los Alamos National Laboratory code ATOMIC which makes no such approximations. As both approximations are used by other astrophysical and low-density modeling codes, the results should be of broad interest. He-like K{alpha} emission spectra are presented for three elements, Ni, Fe, and Ca, in order to gauge the effect of both the statistical methods and the ground-state-only, quasistatic approximation employed in GSM. This work confirms that at and above the temperature of maximum abundance of the He-like ionization stage, the range of validity for both approximations is sufficient for modeling the low- and moderate-density regimes one typically finds in astrophysical and magnetically confined fusion plasmas. However, a breakdown does occur for sufficiently high densities; we obtain quantitative limits that are significantly higher than previous works. Additionally, this work demonstrates that, while the range of validity for both approximations is sufficient to accurately predict the density-dependent quenching of the z line, the approximations begin to break down at higher densities. Thus, these approximations should be used with greater care when modeling high-density plasmas such as those found in laser-driven inertial confinement fusion and electromagnetic pinch devices.},
doi = {10.1103/PHYSREVA.76.062504},
url = {https://www.osti.gov/biblio/21140643}, journal = {Physical Review. A},
issn = {1050-2947},
number = 6,
volume = 76,
place = {United States},
year = {Sat Dec 15 00:00:00 EST 2007},
month = {Sat Dec 15 00:00:00 EST 2007}
}