Title: Effect of higher-order multipole moments on the Stark line shape

Abstract

Spectral line shapes are sensitive to plasma conditions and are often used to diagnose electron density of laboratory plasmas as well as astrophysical plasmas. Stark line-shape models take into account the perturbation of the radiator’s energy structure due to the Coulomb interaction with the surrounding charged particles. Solving this Coulomb interaction is challenging and is commonly approximated via a multipole expansion. Yet, most models include only up to the second term of the expansion (the dipole term). While there have been studies on the higher-order terms due to one of the species (i.e. either ions or electrons), there is no model that includes the terms beyond dipole from both species. Here, we investigate the importance of the higher-order multipole terms from both species on the Hβ line shape. First, we find that it is important to include higher order terms consistently from both ions and electrons to reproduce measured line-shape asymmetry. Next, we study the line shape convergence with the higher-order terms at 1017, 1018, and 1019 e/cc. We discover that the line shape calculated with the dipole-only approximation becomes inaccurate as density increases. It is necessary to include only up to the third (quadrupole) term to compute the line-shapemore » accurately within 2%. Since most existing models include only the dipole terms, the densities inferred with such models are in question. Finally, we investigate the impact of neglecting the quadrupole terms on density diagnostics. We find that the model without the quadrupole term slightly underestimates the density, and the discrepancy becomes as large as 12% at high densities. Although the case of study is limited to Hβ , we expect similar impact on other lines.« less

Authors:

Gomez, T. A. ^[1]; Nagayama, T. ^[2]; Kilcrease, D. P. ^[3]; Montgomery, M. H. ^[1]; Winget, D. E. ^[1]

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+ Show Author Affiliations

1. Univ. of Texas, Austin, TX (United States)
2. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Publication Date:

Tue Aug 02 00:00:00 EDT 2016

Research Org.:

Univ. of Texas, Austin, TX (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Fusion Energy Sciences (FES)

OSTI Identifier:

1511676

Alternate Identifier(s):

OSTI ID: 1280206

Grant/Contract Number:  

NA0003843; SC0010623

Resource Type:

Accepted Manuscript

Journal Name:

Physical Review A

Additional Journal Information:

Journal Volume: 94; Journal Issue: 2; Journal ID: ISSN 2469-9926

Publisher:

American Physical Society (APS)

Country of Publication:

United States

Language:

English

Subject:

74 ATOMIC AND MOLECULAR PHYSICS