Plasma turbulence measured by fast sweep reflectometry on TORE SUPRA

Traditionally devoted to electron density profile measurement we show that fast frequency sweeping reflectometry technique can bring valuable and innovative measurements onto plasma turbulence. While fast frequency sweeping technique is traditionally devoted to electron density radial profile measurements we show in this paper how we can handle the fluctuations of the reflected signal to recover plasma density fluctuation measurements with a high spatial and temporal resolution. Large size turbulence related to magneto-hydrodynamic (MHD) activity and the associated magnetic islands can be detected. The radial profile of the micro-turbulence, which is responsible for plasma anomalous transport processes, is experimentally determined through the fluctuation of the reflected phase signal.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France

On non-zero space average density perturbation effects in tokamak plasma reflectometer signals

12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France)The effects of the non-zero average density perturbation on phase and amplitude measured by reflectometry are presented. The non-zero average density perturbation on the phase variation can be seen as an index effect as soon as the shape of the density perturbation does not introduce spectral effects. Amplitude modulation in time follows generally the properties of the cut-off layer seen as a mirror but some specific situations produce a time modulation two times higher than the input time variation of the density perturbation as observed in Tore Supra. The introduction of secondary cut-off can exhibit this effect as shown in 2D simulations

Formation of spiral structures and radial convection in the edge region of a magnetized rotating plasma

The rotation of a cylindrical plasma column in a magnetic field has been studied in the linear section of the new plasma device Mistral. Under suitable conditions we observe a transition to a turbulent regime characterized by strong, bursty fluctuations at the edge of the column. The detection and the study of the spatio-temporal evolution of structures in the turbulent regime have been performed by means of a new enhanced conditional sampling technique. We have collected evidence of the development of a bent tail emanating from the plasma column. The charged particles inside the structure move along a spiral trajectory resulting in a net radial convection of the plasma to the walls. We show experimentally that a poloidal electric field is present inside the structures leading to the observed outwards radial E × B drift, in agreement with the expectations of recent and past theoretical works

Plasma Dynamics

Contains research objectives and summary of research on nineteen research projects split into five sections.National Science Foundation (Grant ENG75-06242-A01)U.S. Energy Research and Development Administration (Contract E(11-1)-2766)U.S. Air Force - Office of Scientific Research (Grant AFOSR-77-3143)U.S. Energy Research and Development Administration (Contract EY-76-C2-02-3070.*000

Variation en fonction de la température électronique de la composition d'un plasma maxwellien d'azote a basse pression

The composition of a maxwellian nitrogen plasma has been determinated from the rate coefficients of the elementary processes which occur at low pressures. We assume the plasma to be optically thin ; excitations and three-body collisions are neglected. Fifteen processes are considered. The rate coefficients are computed with the generally admitted experimental cross-sections data. By means of a microreversibility formula, the radiative recombination cross-sections are deduced from the photoionization cross-sections. The computation of the rate coefficients has been performed for electron temperature values increasing from 0.2 to 10 eV. Evolution of the plasma ionization state is shown in this temperature range, initiale pressure value being 10-5 torr.La composition d'un plasma d'azote maxwellien est déterminée à partir des coefficients de réaction des processus élémentaires se produisant à basse pression. On suppose le plasma optiquement mince et on néglige les chocs triples et les excitations. Quinze processus sont inclus dans le bilan. Pour le calcul des coefficients de réaction, on utilise les données expérimentales de sections efficaces généralement admises. L'emploi d'une formule de microréversibilité permet de déduire les sections efficaces de recombinaison radiative de celles de photo-ionisation. Le calcul des coefficients de réaction a été effectué pour une température électronique allant de 0,2 à 10 eV. L'évolution de l'état d'ionisation du plasma est représenté dans cet intervalle de température pour une pression initiale de 10-5 torr

Experimental and numerical study of kinetic effects on the upper hybrid resonance cone

International audienc

Étude théorique et expérimentale de l'état d'ionisation d'un plasma d'azote créé par une décharge réflexe à cathodes froides

The ionic densities of a nitrogen plasma are computed from a model in which ionizations are produced by a fast electron beam and recombinations by the thermal electrons. We take into account wall recombination of atomic nitrogen, charge exchange of atomic ions and diffusion of charged particles across a magnetic field. The model is compared with mass spectrometric and microwave measurements obtained in a reflex discharge.On calcule les densités ioniques d'un plasma d'azote à l'aide d'un modèle dans lequel les ionisations sont dues à un faisceau d'électrons rapides, les recombinaisons étant assurées par les électrons thermalisés de plus grande densité. On tient compte de la recombinaison atomique sur les parois, de l'échange de charge de l'ion atomique et de la diffusion des particules chargées à travers un champ magnétique. On compare les résultats du modèle avec des mesures effectuées par spectrométrie de masse et par interférométrie U.H.F. sur une décharge réflexe

Résolution de la relation de dispersion d'un magnétoplasma chaud pour des modes se propageant dans une direction quasi perpendiculaire au champ magnétique

Our aim is to determine the eigenmodes of a warm magnetoplasma which propagates in a direction almost perpendicular to the confining magnetic field. This is done in two ways. First we solve by means of a computer the exact dispersion relation in the complex plane (kc/ωr, ωi/ωH). Secondly, using an approximate equation which is valid for regions outside the vicinity of the cyclotron harmonics, we determine the undamped modes. It can be observed that in cases of almost perpendicular propagation the real high refractive indices previously obtained for perpendicular propagation are still valid. However we find that there is an attenuation of the modes. We have calculated this damping.Nous cherchons les modes propres d'un magnétoplasma chaud en propagation voisine de la perpendicularité au champ magnétique de confinement, soit en résolvant numériquement dans le plan complexe (kc/ωr, ωi/ω H) l'équation de dispersion exacte, soit à l'aide d'une équation approchée valable hors du voisinage des harmoniques cyclotroniques et qui fournit des modes propres non amortis. On constate qu'un écart à la perpendicularité conserve les résonances d'indice réel de la propagation perpendiculaire, par contre les modes sont amortis, et nous avons chiffré cet amortissement

Electrostatic acceleration and ion acoustic instability in the solitary ion beam-plasma slow wave

International audienc

Ballistic impurity ions observed in front of ion acoustic solitons

International audienc