Habilitation a Diriger des Recherches : Caractérisation par spectroscopie d'émission des plasmas de bord des machines de fusion parconfinement magnétique

This manuscript describes some spectroscopic techniques applied to magnetic fusion plasmas. These techniques are based on the use of spectral lines which are affected by Stark and Doppler broadenings and by level-splitting Zeeman effect and allow the determination of the plasma parameters of the emissive plasma. The plasma conditions considered here cover all plasma regimes met in tokamak and stellarator divertors ranging from ionizing (low density, attached plasmas) to recombining plasmas (high-density plasmas detached plasmas). The analysis of the Balmer-alpha of hydrogen and deuterium allow the determination of the neutral sources, the population densities and temperatures of the co-existing neutral classes as well as their fractions. Such parameters are useful for particle recycling evaluation. Being very sensitive to Stark broadening, H/D high-n Balmer lines observed under detachment conditions of divertors are used to determine the electron density of such plasmas. Spectra of lines emitted by carbon impurities from the divertor of JT-60U tokamak under detachment conditions with the presence of an X-point MARFE were also analysed to determine the spatial distribution of the electron density of the divertor plasma. The last application considered here concerns the spectroscopic study of the ablation cloud of a carbon pellet injected in the Large Helical Device (LHD) with a particular focus on the analysis of a C II line affected by Stark broadening.Ce manuscrit décrit quelques techniques spectroscopiques appliquées aux plasmas de fusion magnétique. Elles sont basées sur l'utilisation de spectres de raies qui sont affectées par les élargissements Stark et Doppler et par l'effet Zeeman et permettent de déterminer les paramètres des plasmas émissifs

Accuracy of impact broadening models in low-density magnetized hydrogen plasmas

International audienceThe impact approximation used in the modelling of Stark profiles is examined when a magnetic field is present. Motivated by tokamak plasma spectroscopy, we calculate line shapes and $S$-matrix elements for the first Lyman lines of hydrogen with two models proposed for retaining simultaneously Stark and Zeeman effects in the impact limit. An evaluation of the accuracy of the two approaches is made with the help of a numerical simulation

A table of Balmer gamma line shapes for the diagnostic of magnetic fusion plasmas

International audienc

Broadening of the Neutral Helium 492 nm Line in a Corona Discharge: Code Comparisons and Data Fitting

Passive plasma spectroscopy is a well-established non-intrusive diagnostic technique. Depending on the emitter and its environment which determine the dominant interactions and effects governing emission line shapes, passive spectroscopy allows the determination of electron densities, emitter and perturber temperatures, as well as other quantities like relative abundances. However, using spectroscopy requires appropriate line shape codes retaining all the physical effects governing the emission line profiles. This is required for line shape code developers to continuously correct or improve them to increase their accuracy when applied for diagnostics. This is exactly the aim expected from code–code and code–data comparisons. In this context, the He i 492 nm line emitted in a helium corona discharge at room temperature represents an ideal case since its profile results from several broadening mechanisms: Stark, Doppler, resonance, and van der Waals. The importance of each broadening mechanism depends on the plasma parameters. Here the profiles of the He i 492 nm in a helium plasma computed by various codes are compared for a selected set of plasma parameters. In addition, preliminary results related to plasma parameter determination using an experimental spectrum from a helium corona discharge at atmospheric pressure, are presented

Modeling of Stark–Zeeman Lines in Magnetized Hydrogen Plasmas

International audienc

Stark-Zeeman Line Shape Modeling for Magnetic White Dwarf and Tokamak Edge Plasmas: Common Challenges

International audienc

H-β Line in a Corona Helium Plasma: A Multi-Code Line Shape Comparison

Many spectroscopic diagnostics are routinely used as techniques to infer the plasma parameters from line emission spectra, but their accuracy depends on the numerical model or code used for the fitting process. However, the validation of a line shape code requires some steps: the comparison of the line shape code with other similar codes for some academic (simple) cases and then for more complex ones, the comparison of the fitting parameters obtained from the best fit of the experimental spectra with those obtained with other diagnostic techniques, and/or the comparison of the fitting parameters obtained by different codes to fit the same experimental data. Here we compare the profiles of the hydrogen Balmer β line in helium plasma computed by five codes for a selected set of plasma parameters and we report on the plasma parameters inferred by each of them from the fitting to a number of experimental spectra measured in a helium corona discharge where the pressure was in the range of 1–5 bars

Stark Broadening from Impact Theory to Simulations

International audienc

Line shapes in turbulent plasmas

The fluctuations and oscillations observed in turbulent plasmas may affect the line shapes emitted by atoms and ions. We investigate several plasma conditions for which a spectroscopic signature of plasma turbulence can be observed. Starting from the simple model of microturbulence for Doppler profile, we examine how information on turbulent fluctuations is obtained in astrophysics and magnetic fusion plasmas. We recall the potential of a formalism which expresses the measured line shape in function of the probability density function of the fluctuating plasma parameters. New calculations of hydrogen dipole autocorrelation functions and line shapes are presented for plasmas affected by strong Langmuir turbulence and nonlinear wave collapse. We propose a model using a sequence of envelope solitons for the electric field created by the wave packets and felt by the emitters, and show that the line shape may be dominated by the effect of strong Langmuir turbulence

Line shapes in turbulent plasmas

International audienc