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Nonlinear Dynamics of Magnetic Island Imbedded in Edge Tokamak Plasma Micoturbulence

Nonlinear Dynamics of Magnetic Island Imbedded in Edge Tokamak Plasma Micoturbulence. M. Muraglia , O. Agullo, S. Benkadda , P. Beyer France- Japan Magnetic Fusion Laboratory , LIA 336, France PIIM Laboratory UMR 6633 CNRS/Université de Provence, France X. Garbet

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Nonlinear Dynamics of Magnetic Island Imbedded in Edge Tokamak Plasma Micoturbulence

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  1. Nonlinear Dynamics of Magnetic Island Imbedded in Edge Tokamak Plasma Micoturbulence M. Muraglia, O. Agullo, S. Benkadda, P. Beyer France-JapanMagnetic Fusion Laboratory, LIA 336, France PIIM Laboratory UMR 6633 CNRS/Université de Provence, France X. Garbet IRFM, Association EURATOM CEA, CEA Cadarache, France

  2. Introduction and Motivation • The effects of MHD instabilities and micro-turbulence on plasma confinement have been investigated separately. • However these instabilities usually appear in the plasma at the same time. • - Micro-turbulence is observed in Large Helical Device plasmas • that usually exhibit MHD activities. • K. Tanaka, et al., Nuclear Fusion (2006) • - MHD activities are observed in reversed shear plasmas with a • transport barrier related to zonal flows and micro-turbulence. • Takeji, et al., Nuclear Fusion (2002) • In the present work, we study the interaction between Tearing Modes and a pressure gradient instability (Interchange’s like instability).

  3. Introduction and Motivation produce - Large scale flows - Zonal flows Micro-turbulence stabilize ? Island poloidal rotation ? Macro-MHD Goal : Focus on the nonlinear multi-scale interaction of the fields and get some insight on the origin of island poloidal rotation .

  4. Model • Reduced MHD equations for electrostatic potential , pressure p, and magnetic flux  • Model takes into account both Tearing Mode and Interchange in ‘slab’ geometry (2D). Curvature effects : Dissipation Coefficients: Viscosity Diffusivity resistivity

  5. Dynamics of a Small Island • Time evolution of the energies presents four important regime : • Linear Regime • First nonlinear level • Apparition of a secondary instability (triggered by interchange unstable modes) • Second nonlinear level caracterised by a new equilibrium

  6. Origin of the Poloidal Rotation • Origin of the poloidal rotation : • Electrostatic potential velocity associated to drift velocity • or • Pressure velocity associated to diamagnetic effect • Thanks to generation of small scales, diamagnetic effect produces the • poloidal rotation.

  7. Conclusion • We studied the interaction between magnetic island generated by Tearing instability and an interchange like micro-turbulence. • If the coupling parameter between p and  is strong : • - the Tearing mode is driven by a pressure gradient, • - an interplay between p,  controls the dynamics of the saturated state. • A secondary instability, triggered by interchange unstable modes, appears and generates small scales. Then, the system reaches a new equilibrium. • Diamagnetic effect is generated nonlinearly thanks to the generation of small scales. Diamagnetic effect allows the island poloidal rotation.

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