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• The motional Stark broadening of spectral lines is investigated in the case of plasmas subject to a large external magnetic field. • A line shape model that accounts for atomic velocity changes due to collisions is proposed. • It is shown that such collisions significantly affect the line broadening. The shape of spectral lines in strongly magnetized plasmas is investigated theoretically in the framework of astrophysical research. Under certain conditions, the broadening of lines observed on white dwarf spectra is dominated by the so-called motional Stark effect, which occurs due to the Lorentz electric field v → × B →. If the plasma density is high enough, collisions between the emitter and perturbers change the atomic velocity v → and the resulting motional Stark broadening is modified. We illustrate this modification through dedicated line shape calculations based on a stochastic model for the atomic velocity. A universal line shape formula, which is applicable to any isolated atomic line, is proposed for implementation in line shape codes. [ABSTRACT FROM AUTHOR]

In plasmas coupled to an external energy source like a beam of energetic electrons, one can observe the non‐linear coupling of Langmuir waves with ion sound and electromagnetic waves. This non‐linear interaction of waves changes the structural and radiative properties of plasmas. Coherent wave packets are trapped in regions of high intensity, and are subjected to a wave collapse cycle. We show that the electric field of the wave packets can modify the spectral lines emitted by hydrogen atoms. Our model for this field is a sequence of envelope solitons oscillating at the plasma frequency or the upper hybrid frequency. The calculations presented concern the Hα and Hβ Balmer lines of hydrogen and show the possible modifications of the line shapes if wave collapse conditions affect the edge plasma. [ABSTRACT FROM AUTHOR]

In plasmas subject to a strong magnetic field, the dynamical properties of the microfield are affected by the cyclotron motion, which can alter Stark-broadened lines. We illustrate this effect through calculations of the hydrogen Lyman a line in an ideal one-component plasma. A focus is put on the central Zeeman component. It is shown that the atomic dipole autocorrelation function decreases more slowly if the cyclotron motion is retained. In the frequency domain, this denotes a reduction of the line broadening. A discussion based on numerical simulations and analytical estimates is done. [ABSTRACT FROM AUTHOR]

A summary of results obtained at the third Spectral Line Shape in Plasmas code comparison workshop (SLSP3) is given. As in the SLSP1 and SLSP2, a standardized set of case problems was decided on in advance and then investigated at the workshop. A presentation of these cases, together with a discussion of selected results, is provided here. [ABSTRACT FROM AUTHOR]

• The Stark broadening of hydrogen lines is reexamined in the case of plasmas subject to a large external magnetic field. • It is shown that the energy degeneracy removal due to the diamagnetic Zeeman effect strongly affect the line broadening. • Computer simulations of Lyman and Balmer line shapes in white dwarf atmosphere conditions are performed as an illustration. The Stark broadening of hydrogen lines with a low upper principal quantum number n is reexamined in the case of plasmas subject to a large (≳ 1 kT) external magnetic field. This investigation has been motivated by the observation of strong Zeeman splitting in a significant number of white dwarf spectra. The diamagnetic Zeeman effect term present in the Hamiltonian removes the degeneracy of the energy levels in orbital quantum number l , which results in an alteration of the Stark perturbation due to the microfield. In this work, we investigate this effect by applying a computer simulation method designed for Stark broadening modeling. A focus is put on the Lyman α and H- α lines. Based on line shape calculations, we show that the width of the Zeeman components is strongly dependent on the magnetic field. [ABSTRACT FROM AUTHOR]

Abstract: It is shown that the unified theory for Stark broadening leads to incorrect results when correlated emitter–perturber collisions are present. With a kinetic theory treatment, we propose an extension of the model able to account for such correlations. The treatment presents analogies with renormalization techniques and the resulting collision operator has a structure similar to that obtained within the unified theory. We illustrate the applicability of the model through calculations of hydrogen line shapes in ideal cases. [Copyright &y& Elsevier]

Abstract: We investigate the role of turbulent fluctuations on line shape formation in optically thin plasmas. A general expression, valid if the turbulent scales are much larger than the atomic scales, is obtained for the profile measured using a passive spectroscopy set up. Well-known limiting cases for Doppler and Stark broadening are identified. Then, the role of temperature fluctuations on Doppler line shapes, and the effect of density fluctuations on Stark broadened lines in the quasi-static regime are investigated. [Copyright &y& Elsevier]

• Computer simulations employed in Stark broadening calculations are reexamined within the perspective of giving error bars to results. • A variance estimator is applied to the quantification of the statistical noise present on simulated line shapes. • Two expressions for the radiated power spectrum, which are analytically equivalent but lead to different noise levels, are examined in detail. Computer simulations employed in Stark broadening calculations are reexamined within the perspective of giving error bars to results. As a rule, the calculated spectra exhibit a noisy structure, which is inherent to the random number generators involved in the numerical method. Using a variance estimator, we quantify the statistical noise on simulated line shapes. Two expressions for the radiated power spectrum, which are analytically equivalent but lead to different noise levels, are considered. A discussion of this difference is carried out based on an analytical model. [ABSTRACT FROM AUTHOR]

Stochastic processes provide flexible and fast calculations for modeling dynamical interactions between an atom and charged particles. We use a stochastic renewal process for the plasma microfield being the cause of Stark broadening. The accuracy and improvement possibilities of Lyman profiles calculations with a renewal process are analyzed by comparing to ab initio simulations for ion broadening only. Stochastic processes may also be applied to out of equilibrium plasmas. We present our first results for the effect of Langmuir waves on a line broadened by electrons only, and for the changes of atomic populations submitted to strong temperature fluctuations. [ABSTRACT FROM AUTHOR]

Abstract: An overview of several spectral line shapes studies of common interest in astrophysical and laboratory plasmas is presented. For lines dominated by Stark broadening, approaches taking into account the dynamics of numerous perturbers are sometimes required. We briefly recall ab initio simulation techniques and model microfield methods used for such conditions. Together with the impact approximation, such models may also be used for studying the effects on a line profile of a magnetic field of the order of the tesla, allowing the diagnostic of stellar objects or magnetic fusion devices. The problem of the apparent spectral line emitted in a plasma affected by strong fluctuations of the plasma parameters is discussed for the case of optically thin plasmas. [Copyright &y& Elsevier]