Influence of Microfield Directionality on Line Shapes

Abstract

In the framework of the Spectral Line Shapes in Plasmas Code Comparison Workshop (SLSP), large discrepancies appeared between the different approaches to account for ion motion effects in spectral line shape calculations. For a better understanding of these effects, in the second edition of the SLSP in August, 2013, two cases were dedicated to the study of the ionic field directionality on line shapes. In this paper, the effects of the direction and magnitude fluctuations are separately analyzed. The effects of two variants of electric field models, (i) a pure rotating field with constant magnitude and (ii) a time-dependent magnitude field in a given direction, together with the effects of the time-dependent ionic field on shapes of the He II Lyman-α and-β lines for different densities and temperatures, are discussed.

The Application of the Cut-Off Coulomb Model Potential for the Calculation of Bound-Bound State Transitions

“…Here, g(ω, ω f i ) is the spectral line profile and could be obtained, for instance, as a result of a molecular dynamics (MD) simulations [20][21][22] or as a result of theoretical modeling and spectral line data [23][24][25][26][27]. The lineshape is normalized to unity area, e.g.,…”

Special Issue on Spectral Line Shapes in Plasmas

“…Now, Ferri et al [3] discuss this, extending the analysis to more complex transitions with forbidden components. The ion dynamics effect is intimately related to the microfield directionality, as studied in depth by Calisti et al [4]. Notably, the effects of the directionality of the microfield fluctuations were first researched within the framework of the "standard theory" of the plasma line broadening almost four decades ago, but have largely been forgotten.…”

Spectral-Kinetic Coupling and Effect of Microfield Rotation on Stark Broadening in Plasmas

“…The basics of the theory of thermal corrections for Stark profiles along with the results of [7][8][9]12,[23][24][25] are given in Section 3. Later, the predictions, given in [12,[23][24][25] about significance of microfield rotation effects in ion dynamics, were confirmed within other approaches [30,33], but until now it has not been explicitly shown in the results of computer simulations (see also [75]). In the present work, simultaneously with [75], the approximate way to separate microfield rotation effects in the profile of Ly-alpha within MD simulations is realized and described in Section 4.…”

“…This allowed the beginning of profound detailed comparisons of various computer codes developed for calculation of spectral lines profiles in plasmas, which was the main purpose of the first two SLSP workshops [74]. However, the understanding and comparison of realizations of most successful contemporary codes on a wide set of physical cases (see [74][75][76][77] and other articles of this issue) give good reason to once more discuss, check, and revise the physical notions and ideas which form the foundation of the contemporary theory of spectral line broadening by plasmas. The present article pursues these aims.…”

“…The other problem is related to the attempts to separate the influence of microfield fluctuations on Stark profiles into two components, perpendicular and parallel to the microfield direction [5,6], in order to separate the contribution from microfield rotation effects [12,[23][24][25]30,33], predicted to be dominating in the central part of the line [23][24][25]. The necessity of this discussion arose when it was recently shown that existing approaches to accounting for ion dynamics give results that differ from one another [74][75][76]. This inspired attempts to describe ion dynamics effects in terms of physical mechanisms, instead of practically tacit conventional numerical comparison of complicated simulations that began with the first works done using the Model Microfield Method (MMM) in the 1970s [14,15,28,29].…”