Projet ANR-06-BLAN-0084 – STUDY FUS : Dynamique locale et échelles de la turbulence dans les plasmas de fusion. Scales and TUrbulence DYnamics in FUSion plasma
Programme : Programme blanc (BLANC) 2006
Année de financement : 2006
Coordinateur du projet : CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE ILE-DE-FRANCE SECTEUR OUEST ET NORD (CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE ILE-DE-FRANCE SECTEUR OUEST ET NORD)
Partenaires : Centre national de la recherche scientifique; Centre national de la recherche scientifique; Commissariat à l'énergie atomique et aux énergies alternatives
Montant : 480000.0 euros
Date de début : 2006
Durée : 36 mois
Résumé : Fusion energy shows great promise to contribute, as a sustainable energy source, to the growing energy needs of populations, with limited environmental impact (no greenhouse gases or long lived waste, intrinsic safety). It is also a scientific and engineering challenge. In magnetic fusion device such as tokamaks, high temperature plasma is confined by strong magnetic fields to reach the thermonuclear conditions. The international project ITER which will be hosted by France at Cadarache, aims at its demonstration. However the quality of confinement is degraded by turbulence. Turbulent transport conditions the dimensioning of a fusion reactor and thus its economical viability. Understanding and controlling this turbulence is thus a major goal in magnetic fusion research.  Plasma turbulence shares the non linear characters of fluid turbulent flows, with the further complexity of the coupling between electromagnetic fields and charged particles trajectories. The complex dynamics of these fluid and plasma flows leading to intermittent behaviour, the wide temporal and spatial scales involved make them difficult to model accurately. Beyond the fundamental question it rises, the practical implications are crucial for predicting fluid mixing properties or turbulent transport in tokamaks. A large modelling effort in fluids and plasma has developed worldwide, which reflects in the number of projects proposed and supported by the Agence Nationale de la Recherche last year.  This understanding requires experimental effort as well. Detailed fluctuation measurements provide key elements for validating the models and improving their predictive capabilities. The knowledge of turbulent scales is especially crucial for identification of instabilities implicated that might have different drives and scales. Also the question of turbulence control is a very active field. It has been observed experimentally that appropriate shearing of flows or magnetic field shear can strongly reduce the turbulent transport, and result in transport barriers. Also self-generated flows can regulate the transport. Fluctuations measurements are thus necessary to increase our understanding of these mechanisms and elaborate novel control methods.  The project will make possible the detailed study of the rapid dynamics of the fluctuations with wide spatial and spectral coverage in the Tore Supra tokamak. Two different techniques will be implemented, both using millimetric waves for probing the hot magnetised plasma, in the frequency range where the wave encounters a reflection layer: reflectometry and wave scattering close to a reflection layer, in the high performance applications developed here, yields complementary spectral sensitivity and high temporal resolution. Indeed the first one will measure a complete density profile on a time scale smaller than the turbulence correlation time, and capture the fast dynamics of radial structures. Wave scattering close to the cut-off directly provides the spatial Fourier analysis of the fluctuations in the ortho-radial direction. The novel double polarisation system will permit to get the full fluctuation wave-number spectrum, from low to high k, and their dynamics, from the Doppler effect. The same frequency band will be used for covering the same spatial region, which ensures the synergy between the two diagnostics.   These techniques are novel by their high temporal and spatial resolution and their ability to explore turbulent scales. All plasma measurements are intrinsically difficult, for the high temperatures in the plasma core preclude the use of any solid material measuring instrument. The techniques must be indirect, from outside the plasma. Active techniques, observing the effect of the plasma on a source of applied radiation or particles are more suitable for localised measurements. Turbulence exploration remains very limited in the plasma core, while it has been much more developed at the edge, where Langmuir probes .