Méthodes de reconstruction du profil de densité pour la réflectométrie en mode extraordinaire

The goal of this PhD is to improve the data analysis techniques of frequency swept reflectometry for determination of the density profile of fusion plasmas. There has been significant improvements in the last two decades on the hardware design and signal extraction techniques, but the data analysis is lagging behind and require further improvements to meet the required standards for continuous operation in future reactors. The improvements obtained in this thesis on the reconstruction of density profiles provide a better accuracy in a shorter time, even in the presence of a density hole, also enabling sufficiently precise measurements of the properties of turbulence used to validate numerical models, and allowing real-time monitoring of the shape and position of the plasmaLe but de cette thèse est d'améliorer les techniques d'analyse de données de la réflectométrie à balayage de fréquence pour la détermination du profil de densité des plasmas de fusion. Au cours des deux dernières décennies, des améliorations significatives ont été apportées sur la partie matérielle et sur d'extraction des signaux, mais l'analyse des données est en retard et nécessite d'autres améliorations pour répondre aux spécifications exigées pour un fonctionnement en continu des futurs réacteurs. Les améliorations obtenues lors de ce travail de thèse sur la reconstruction des profils de densité fournissent une meilleure précision en un temps plus court ceci même en présence de trou de densité conduisant à une mesure des propriétés de la turbulence suffisamment précise pour valider des modèles numériques et permettant la surveillance en temps réel de la forme et de la position du plasm

New density profile reconstruction methods in X-mode reflectometry

International audienceThe reconstruction method published by Bottollier-Curtet and Ichtchenko in 1987 has been the standard method of density profile reconstruction for X-mode reflectometry ever since, with only minor revision. Envisaging improved accuracy and stability of the reconstruction method, functions more complex than the linear are evaluated here to describe the refractive index shape in each integration step. The stability and accuracy obtained when using parabolic and fixed or adaptative fractional power functions are compared to the previous method and tested against spurious events and phase noise. The developed relation from the plasma parameters to the best integration shapes allows for optimization of the reconstruction for any profile shape. In addition, the density profiles can be reconstructed using less probing frequencies without accuracy loss, which speeds up the reconstruction algorithm and enables real-time monitoring of faster density profile evolution

Electromagnetic wave behaviour in turbulent plasmas as a possible support for diagnosing fusion plasma properties

International audience- Why to study the turbulence in Fusion Plasmas and to do what with this?- What are the scales to consider, using probing electromagnetic waves?- What are the possible ways to describe wave-turbulence interaction?- What are the diagnostics to probe turbulence in Fusion Plasmas?- How do they operate, under which plasma conditions?- What is the status of the code development in 3D?- Conclusion

Recent progress in L-H transition studies at JET: Tritium, Helium, Hydrogen and Deuterium

We present an overview of results from a series of L-II transition experiments undertaken at JET since the installation of the ITER-like-wall (JET-ILW), with beryllium wall tiles and a tungsten divertor. Tritium, helium and deuterium plasmas have been investigated. Initial results in tritium show ohmic L-H transitions at low density and the power threshold for the L-H transition (P-LH) is lower in tritium plasmas than in deuterium ones at low densities, while we still lack contrasted data to provide a scaling at high densities. In helium plasmas there is a notable shift of the density at which the power threshold is minimum ((n) over bar (e,min)) to higher values relative to deuterium and hydrogen references. Above (n) over bar (e,min) (He) the L-H power threshold at high densities is similar for D and He plasmas. Transport modelling in slab geometry shows that in helium neoclassical transport competes with interchange-driven transport, unlike in hydrogen isotopes. Measurements of the radial electric field in deuterium plasmas show that E-r shear is not a good indicator of proximity to the L-H transition. Transport analysis of ion heat flux in deuterium plasmas show a non-linearity as density is decreased below (n) over bar (e,min). Lastly, a regression of the JET-ILW deuterium data is compared to the 2008 ITPA scaling law