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Pré-Publication, Document De Travail Année : 2004

Characterization of low frequency instabilities and study of their transition to turbulence in a magnetized plasma column

Résumé

In this contribution we report on experiments performed on the low-b plasma device MIRABELLE. Using a limiter, we recently got experimental evidence that when increasing the magnetic field transitions between various gradient driven instabilities are observed. The characterization is based on: (i) comparison between the poloidal propagation velocity and the diamagnetic and E´B velocities deduced from measurements of the density and plasma potential profiles; (ii) measurements of the axial wave number. Moreover, these results are corroborated by measurements of the radial variation of the phase of the fluctuations. More precisely, at low magnetic field the strong Er´B velocity shear drives a Kelvin-Helmholtz instability, whereas at higher magnetic field drift waves are only observed [1]. In between we also observed in some cases a centrifugal (Rayleigh-Taylor) instability. With regards to the role played by these instabilities in non-diffusive transport processes in plasma fusion experiments, and aiming at characterizing the turbulent transport, we studied the transition from regular regimes to spatiotemporal chaos and turbulence. We demonstrate that for the Kelvin-Helmholtz instability the transition to turbulence follows the quasi-periodicity (Ruelle-Takens-Newhouse) route, as previously observed for drift waves [2]. Moreover, temporal analysis of the quasi-periodic regime gives clear evidences of an autonomous periodic pulling regime, i.e. incomplete entrainment. Recent results about the transition to turbulence for a Rayleigh-Taylor instability will also be presented.
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Dates et versions

hal-00001814 , version 1 (22-10-2004)

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  • HAL Id : hal-00001814 , version 1

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F. Brochard, Gildas Bonhomme, E. Gravier. Characterization of low frequency instabilities and study of their transition to turbulence in a magnetized plasma column. 2004. ⟨hal-00001814⟩
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