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Nouvelle traduction : Avalanches and the edge of chaos in subcritical gyrokinetic systems

par Caroline CHAMPENOIS - publié le

mardi 4 septembre, de 10:00 à 16:00, en salle 361

Shearless Transport Barriers in Tokamaks
Iberê L. Caldas
Institute of Physics, University of São Paulo, Brazil

In tokamaks, internal transport barriers, produced by modifications of the plasma current profile, reduce particle transport and improves plasma confinement. However, besides the progress to understand this reduction, the triggering of internal transport barriers and its dependence with the plasma profiles is still under investigation. We consider that the onset of shearless invariant curves inside the plasma form a kind of internal transport barriers. We investigate the influence of equilibrium profiles on these shearless barriers onset for a non-integrable drift-kinetic model, for large aspect ratio tokamaks, used to describe particle transport driven by drift waves.

Bursts in plasma turbulence at TCABR Tokamak and Texas Helimak
Zwinglio Guimarães-Filho
Instituto de Física da Universidade de São Paulo - Brazil

The turbulence in the edge region of magnetically confined plasmas presents large density fluctuations with standard deviation comparable with the mean value, in which density peaks with amplitude several standard deviations above the mean are often observed. These density peaks (generically called bursts) are related with the propagation of coherent structures with sizes much larger than the turbulent characteristic length and play an important role on the overall particle and energy turbulent transport in the edge region of tokamaks. We studied the behavior of these structures in the TCABR tokamak (University of São Paulo, Brazil) and in Texas Helimak (University of Texas at Austin, USA). In both devices, we used Langmuir probes to observe the bursts and their average profiles were determined from conditional average around the time of the density peaks. In TCABR, a 1D array of probes was used, while in Texas Helimak, a large 2D grid of probes allows a precise determination of the burst spatial profiles and its propagation properties. The 2D analysis shows that time delays determined from 1D arrays are not suitable to evaluate the burst propagation properties, leading to erroneous velocity estimations.

A reduced model to predict EGAM-induced particle transport
David Zarzoso
Aix-Marseille université and CNRS

Effect of isotope mass on transport and confinement :
overview of theoretical interpretations and current status of modelling

Yann Camenen
Aix-Marseille université and CNRS

Experimentally, the beneficial impact of the isotope mass on the energy confinement time is well established in magnetic fusion devices. Explaining this isotope dependence, however, remains a challenge. The purpose of this talk is to review the existing interpretations and summarize the current understanding of this research from a theoretical perspective.

I. Caldas et Z. Guimarães sont au laboratoire jusqu’au vendredi 7 septembre.
Contact : Y. Elskens


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