Synergetic effects of collisions, turbulence and sawtooth crashes on impurity transport

This paper investigates the interplay of neoclassical, turbulent and MHD processes, which are simultaneously at play when contributing to impurity transport. It is shown that these contributions are not additive, as assumed sometimes. The interaction between turbulence and neoclassical effects leads to less effective thermal screening, i.e. lowers the outward flux due to temperature gradient. This behavior is attributed to poloidal asymmetries of the flow driven by turbulence. Moreover sawtooth crashes play an important role to determine fluxes across the q = 1 surface. It is found that the density profile of a heavy impurity differs significantly in sawtoothing plasmas from the one predicted by neoclassical theory when neglecting MHD events. Sawtooth crashes impede impurity accumulation, but also weaken the impurity outflux due to the temperature gradient when the latter is dominant

MHD measurements in the von Kármán sodium experiment

We study the magnetic induction in a confined swirling flow of liquid sodium, at integral magnetic Reynolds numbers up to 50. More precisely, we measure in situ the magnetic field induced by the flow motion in the presence of a weak external field. Because of the very small value of the magnetic Prandtl number of all liquid metals, flows with even modest Rm are strongly turbulent. Large mean induction effects are observed over a fluctuating background. As expected from the von Kármán flow geometry, the induction is strongly anisotropic. The main contributions are the generation of an azimuthal induced field when the applied field is in the axial direction ~an V effect! and the generation of axial induced field when the applied field is the transverse direction ~as in a large scale a effect!. Strong fluctuations of the induced field, due to the flow nonstationarity, occur over time scales slower than the flow forcing frequency. In the spectral domain, they display a f21 spectral slope. At smaller scales ~and larger frequencies! the turbulent fluctuations are in agreement with a Kolmogorov modeling of passive vector dynamics

Collisional and Radiative Processes in Optically Thin Plasmas

Most of our knowledge of the physical processes in distant plasmas is obtained through measurement of the radiation they produce. Here we provide an overview of the main collisional and radiative processes and examples of diagnostics relevant to the microphysical processes in the plasma. Many analyses assume a time-steady plasma with ion populations in equilibrium with the local temperature and Maxwellian distributions of particle velocities, but these assumptions are easily violated in many cases. We consider these departures from equilibrium and possible diagnostics in detail

A class of basis functions for non-ideal magnetohydrodynamic computations

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Kinetic equation of finite Hamiltonian systems with integrable mean field

In this paper, we propose a kinetic theory of finite systems, and a new equation for their « microscopic » average behaviour. The equations of particle motion are supposed to be integrable in the mean collective field or/and in an outside given field. The collision time is assumed to be longer than the characteristic orbital time which rules out a local theory of the Fokker-Planck, or Balescu-Lenard type. Two applications of our equation are foreseen : a finite plasma with a Debye length comparable or larger than its size ; a self confined gravitational system (i.e. a globular cluster) which is always a dilute system with a finite number of stars ; we discuss the validity of a statistical description of such a physical system.Nous proposons dans cet article une théorie cinétique des systèmes finis, ainsi qu'une nouvelle équation pour leur comportement « microscopique » moyen. Le mouvement est supposé integrable dans le champ moyen, collectif et/ou imposé de l'extérieur. On suppose le temps de collision plus grand que les périodes caractéristiques du mouvement moyen, ce qui exclut une approche locale de type Fokker-Planck, ou Balescu-Lenard. On peut citer comme exemple un plasma de taille comparable à la longueur de Debye, ou un système gravitationnel auto-gravitant (amas globulaire), qui est un système dilué contenant un nombre fini d'étoiles. Nous discutons les conditions de validité d'une description statistique de ce type de système

Estimation de l'energie photosynthetiquement active absorbee par une culture de ble a partir de donnees radiometriques

Document interne *INRA, Station de Bioclimatologie Montfavet (FRA) Diffusion du document : INRA, Station de Bioclimatologie Montfavet (FRA)National audienc

Estimation de l'energie photosynthetiquement active absorbee par une culture de ble a partir de donnees radiometriques

Document interne *INRA, Station de Bioclimatologie Montfavet (FRA) Diffusion du document : INRA, Station de Bioclimatologie Montfavet (FRA)National audienc

MHD stability of (2,1) tearing mode: an issue for the preforming phase of Tore Supra non-inductive discharges

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