Control of instabilities and turbulence by fast particles in fusion plasmas

Abstract : Turbulence and MHD instabilities can cause particle and energy transport from core to edge plasma in tokamaks. A consequence is the degradation of plasma confinement. Understanding and controlling those phenomena is of tremendous importance in view of next step fusion experiments such as ITER and DEMO. Fast ions, such as alpha particles or those ions generated by heating sources, are known to have direct and/or indirect interactions with turbulence and MHD instabilities. They may be used to control those phenomena. In this thesis, we study the interaction of fast particles with two different modes: the sawtooth instability; and the Ion Temperature Gradient (ITG) turbulence via the excitation of Energetic particle driven Geodesic Acoustic Modes (EGAMs). First, we report on the strong stabilization of sawteeth by fast deuterium ions, accelerated to the 100 keV range by neutral beam injection and subsequently to the MeV range by 3rd harmonic ion cyclotron resonance heating, in the JET tokamak. This stabilization is analysed and understood in the framework of a theoretical model (Porcelli's model). Second, we perform an analytical study of the linear excitation by fast ions of the electrostatic branch of EGAMs. In particular, by scanning the parameter space, we shed light on the relation and differences between EGAMs and Geodesic Acoustic Modes (GAMs). The latter are known to efficiently interact with turbulence but are harder to control than EGAMs. A good knowledge of this relation is of interest to understand whether GAMs and EGAMs are capable of similar interactions with turbulence. Finally, we use a three wave parametric decay model to study the interaction between EGAMs and ITG modes. The possible control of ITG turbulence by EGAMs is discussed in this framework.
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Submitted on : Saturday, February 20, 2016 - 6:36:07 PM
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Jean-Baptiste Girardo. Control of instabilities and turbulence by fast particles in fusion plasmas. Plasma Physics [physics.plasm-ph]. Ecode doctorale de l'Ecole Polytechnique (EDX), 2015. English. ⟨tel-01276865⟩

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