N. Kasuya and K. Itoh


Two-dimensionally Steep Structure of the Electric Field in Tokamak H-mode

Date of publication:

Oct. 2006

Key words:

21 IAEA Fusion Energy Conference , TH/P6-17


The rapid formation of a density pedestal on an L/H transition has been raising a question why the rapid density evolution is induced. Formation of a poloidal shock structure is predicted in H-mode transport barriers, and consideration of the two-dimensional structure both in the radial and poloidal directions is inevitable to clarify the formation mechanism of the H-mode pedestal. The analyses are carried out with edge plasmas in tokamak H modes, which are induced either spontaneously or by electrode biasing. Two-dimensional structures of the potential, density and flow velocity are calculated with the momentum conservation equation. The validity of the one-dimensional L/H transition theory and the iterative process to obtain the two-dimensional structure are confirmed by our analysis. A steep electric field structure both in the radial and poloidal directions is obtained. The two-dimensional electric field induces radial ion fluxes, which increase in the H-mode transport barrier and affect the electric field. If the Boltzmann relation is violated, radial electron fluxes are induced, and affect the density evolution. Reduction of anomalous transport by the steep gradient of the radial electric field, and generation of the particle fluxes associated with the two-dimensional structure influence the rapid formation of the steep gradients in H-mode plasmas. A transport model including both effects is constructed to reveal the self-consistent mechanism of the density pedestal formation in the L/H transition.

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