Drift wave versus interchange turbulence in tokamak geometry: Linear versus nonlinear mode structure
- Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, D-85748 Garching (Germany)
The competition between drift wave and interchange physics in general E-cross-B drift turbulence is studied with computations in three-dimensional tokamak flux tube geometry. For a given set of background scales, the parameter space can be covered by the plasma {beta} and drift wave collisionality. At large enough plasma {beta} the turbulence breaks out into ideal ballooning modes and saturates only by depleting the free energy in the background pressure gradient. At high collisionality it finds a more gradual transition to resistive ballooning. At moderate {beta} and collisionality it retains drift wave character, qualitatively identical to simple two-dimensional slab models. The underlying cause is the nonlinear vorticity advection through which the self-sustained drift wave turbulence supersedes the linear instabilities, scattering their structure apart before they can grow, imposing its own physical character on the dynamics. This vorticity advection catalyses the gradient drive, while saturation occurs solely through turbulent mixing of pressure disturbances. This situation persists in the whole of tokamak edge parameter space. Both simplified isothermal models and complete warm ion models are treated.
- OSTI ID:
- 20764313
- Journal Information:
- Physics of Plasmas, Vol. 12, Issue 6; Other Information: DOI: 10.1063/1.1917866; (c) 2005 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
- Country of Publication:
- United States
- Language:
- English
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