Dynamic Stark broadening as the Dicke narrowing effect

Studies of spectral line merging in a laser-induced hydrogen plasma diagnosed with two-color Thomson scattering

Laser-induced hydrogen plasma in the density and temperature range of (0.1-5)×10^{23}m^{-3} and (6000-20000)K, respectively, was precisely diagnosed using two-color Thomson scattering technique, inferring the electron number density, electron temperature as well as ion temperature. Simultaneously, spectra of the Balmer series of spectral lines from H-β to H-ζ were measured and plasma emission coefficient calculated within the quasicontiguous frequency-fluctuation model. The theoretical spectra are found to be in good agreement with experimental ones, including higher-density data where discrete lines were observed to merge forming a continuum.

Spectral Modeling of Hydrogen Radiation Emission in Magnetic Fusion Plasmas

Modeling of the spectral line and continuum radiation emitted by hydrogen isotopes in peripheral regions of magnetic fusion is presented through profiles of the Zeeman-Doppler broadened Hα/Dα line and those of the Stark broadened high-n Balmer lines extending beyond the series limit for recombining plasmas. The Hα/Dα line profiles should be modelled while accounting for several populations of neutrals to mimic real situations and analyze experimental data for isotopic ratio determination. On the other side, high-n Balmer lines of hydrogen are used for plasma electron density and temperature diagnostics. Moreover, modelling whole spectra including the continuum radiation contributes to the development of synthetic diagnostics for future magnetic fusion devices for which they can give predictive results through coupling to numerical simulation tools.

A New Procedure to Determine the Plasma Parameters from a Genetic Algorithm Coupled with the Spectral Line-Shape Code PPP

A method of analysis of experimental spectra for obtaining the plasma parameters is presented and discussed. Based on the coupling of the spectral line-shape code PPP with the genetic algorithm PIKAIA, the proposed method is inspired by natural selection mechanisms resulting in the development of basic genetic operators. The spectra analysis is performed by fitting experimental spectra with synthetic spectral line profiles obtained by using theoretical models and a set of plasma parameters, such as its temperature and electron density. In the present paper, the diagnostic procedure based on a genetic algorithm coupled with the PPP code has been used for the analysis of both hydrogen Balmer-β and He I 492.2 nm lines in the helium plasma created by corona discharge. The broadening of these spectral lines due to the Stark effect has been considered, together with the Van der Waals and instrumental broadening.

Plasma pressure broadening for few-electron emitters including strong electron collisions within a quantum-statistical theory

To apply spectroscopy as a diagnostic tool for dense plasmas, a theoretical approach to pressure broadening is indispensable. Here, a quantum-statistical theory is used to calculate spectral line shapes of few-electron atoms. Ionic perturbers are treated quasistatically as well as dynamically via a frequency fluctuation model. Electronic perturbers are treated in the impact approximation. Strong electron-emitter collisions are consistently taken into account with an effective two-particle T-matrix approach. Convergent close-coupling calculations give scattering amplitudes including Debye screening for neutral emitters. For charged emitters, the effect of plasma screening is estimated. The electron densities considered reach up to n(e) = 10(27) m(-3). Temperatures are between T = 10(4) and 10(5) K. The results are compared with a dynamically screened Born approximation for Lyman lines of H and H-like Li as well as for the He 3889 Å line. For the last, a comprehensive comparison to simulations and experiments is given. For the H Lyman-α line, the width and shift are drastically reduced by the Debye screening. In the T-matrix approach, the line shape is notably changed due to the dependence on the magnetic quantum number of the emitter, whereas the difference between spin-scattering channels is negligible.

Quasicontiguous frequency-fluctuation model for calculation of hydrogen and hydrogenlike Stark-broadened line shapes in plasmas

We present an analytical method for the calculation of shapes of Stark-broadened spectral lines in plasmas, applicable to hydrogen and hydrogenlike transitions (including Rydberg ones) with Δn>1. The method is based on the recently suggested quasicontiguous approximation of the static Stark line shapes, while the dynamical effects are accounted for using the frequency-fluctuation-model approach. Comparisons with accurate computer simulations show excellent agreement.

Influence of correlated collisions on Stark-broadened lines in plasmas

An investigation of spectral line broadening in plasmas is carried out within a kinetic-theory approach, based on the Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy. The model employs a resummation procedure to account for correlated emitter-perturber collisions. Applications to hydrogen lines indicate that such collisions strongly affect the width and the shape in the core region. This argument is supported by comparisons to numerical simulations. It is also shown that the usual collision operator models, based on a binary description of emitter-perturber collisions, can be extremely inaccurate. The present model, in a better agreement with numerical simulations, is suggested as an extension suitable for the design of fast and accurate numerical routines for plasma diagnostics.

Frequency-fluctuation model applied to Stark-Zeeman spectral line shapes in plasmas

A very fast method for calculating line shapes in the presence of an external magnetic field accounting for charge particle dynamics is proposed. It is based on a reformulation of the frequency fluctuation model, which provides an expression of the dynamic line shape as a functional of the static distribution function of frequencies. In the presence of an external magnetic field, the distribution of intensity and polarization of the emission depends on the angle between the observation line and the magnetic field's direction. Comparisons with numerical simulations and experimental results for various plasma conditions show very good agreement. Results on hydrogen lines in the context of magnetic fusion and the Lyman-α line, accounting for fine structure, emitted by argon in the context of inertial fusion, are also presented.