Diagnostic spectroscopique des plasmas de fusion magnétique : application à ITER

Cette thèse porte sur la modélisation du rayonnement de raies émis par les plasmas de fusion magnétique pour faire des applications au diagnostic. Une attention particulière est apportée aux électrons découplés (« runaway »), qui sont attendus avec une proportion significative dans ITER. Dans le premier chapitre, nous donnons une introduction générale sur la fusion magnétique et sur les machines tokamak, ainsi que sur les disruptions ; ces dernières sont engendrées par des instabilités et elles peuvent conduire à la formation de faisceaux d’électrons runaway très énergétiques. Dans le deuxième chapitre, le formalisme utilisé dans les modèles d'élargissement de raies spectrales est présenté, à partir d’outils de mécanique quantique et de physique statistique. Des calculs numériques de raies de Balmer sont également effectués dans le cadre d’une application aux diagnostics synthétiques. Dans le troisième chapitre, nous discutons de la physique relative aux ondes de Langmuir, notamment, l’amortissement Landau et son processus inverse, l’instabilité faisceau-plasma. Ce processus engendre un champ électrique oscillant, dont l’amplitude peut être évaluée à l’aide de la théorie quasi-linéaire. Nous présentons cette théorie ainsi qu’une généralisation aux régimes fortement non linéaires dans lesquels les ondes de Langmuir sont couplées aux ondes sonores et électromagnétiques. Enfin, dans le quatrième chapitre, nous appliquons le formalisme pour différentes densités de faisceau dans des conditions de plasma de bord de tokamak et nous examinons la faisabilité d’un diagnostic spectroscopique des électrons runawayThis thesis focuses on the modeling of the atomic line radiation emitted by magnetic fusion plasmas for diagnostic purposes. An improvement of the accuracy of diagnostics is proposed, in order to have a better characterization of runaway electrons in the context of ITER preparation. In the first chapter, we discuss about fusion reaction, about how it is produced in tokamak machines, and we discuss about the disruptions, which are a consequence of instabilities. They are one cause of runaway electrons. In the second chapter, the formalism used in spectral line broadening models is introduced based on quantum mechanics and statistical physics. Numerical calculations are also presented. They are done for applications to synthetic diagnostics in tokamak divertor plasma conditions. Hydrogen Balmer lines with a moderate principal quantum number are considered. In the third chapter, we discuss the physics underlying Langmuir waves. This includes the Landau damping process and its inverse counterpart, the plasma-beam instability mechanism. It is possible to calculate the magnitude of the electric field which is created by a beam of electrons using the quasilinear theory. We present this theory and we present a generalization to strongly nonlinear regimes for which the Langmuir waves are coupled with the ion sound and electromagnetic waves. Finally, we discuss this model and, next, apply the formalism for different beam densities in tokamak edge plasmas and we examine the possibility for making a diagnostic of runaway electrons based on atomic spectroscopy in the fourth chapte

Spectroscopic models for the characterization of energetic particle beams in tokamak edge plasmas

International audienc

Effect of Turbulence on Line Shapes in Astrophysical and Fusion Plasmas

International audienc

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

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