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The non-adiabatic response of passing electrons near mode rational surfaces in strongly magnetized plasmas of tokamak fusion reactor

Julien Dominski

à 11h en salle C. Brot

The tokamak is a magnetic fusion reactor prototype in which the hot plasma (>10 keV) is confined in a closed magnetic field of toroidal geometry. In this kind of fusion reactor, the plasma turbulence and its associated transport are limiting the magnetic confinement of heat and particles. Understanding the turbulence basic mechanisms is thus a key motivation toward the path of controlling fusion as a source of energy. The particular mechanisms which will be presented here concerns the non-adiabatic response of the passing electron dynamics near mode rational surfaces, for typical plasma regimes dominated by micro-turbulence of electrostatic kind : the ion temperature gradient and the trapped electron mode. The turbulent plasma dynamics is described within the gyrokinetic framework, which is based on a 5D reduction of the Vlasov equation, and the electrostatic field is solved with Poisson equation in the quasi-neutral limit. Let us precise that mode rational surfaces are magnetic surfaces on which each magnetic field line is closed one itself, and passing electrons are the electrons which circulate all over the magnetic surface, in opposition to trapped electrons which are mirror-trapped on the outer side of the torus where the magnetic field amplitude is the lowest. The role of passing electrons will thus be revealed by studying its effects on the turbulence transport, in geometry of increasing complexity : from a local linear dispersion relation towards non-linear gyrokinetic simulations of the "Tokamak à Configuration Variable" (TCV). Let us precise that TCV is one of three medium size tokamaks of the european fusion program.