NIFS-399

FULL TEXT (PDF, 1476 KB)


Author(s):

K. Itoh, S-I. Itoh, A. Fukuyama and M. Yagi

Title:

Theory of Self-Sustained Turbulence in Confined Plasmas

Date of publication:

Feb. 1996

Key words:

plasma turbulence, anomalous transport, bifurcation, structural formation, Self-sustained turbulence, radial electric field, improved confinement, simulation

Abstract:

This article overviews some aspect of the recent theoretical activities in Japan on the problem of turbulent transport in confined plasmas. The method of self-sustained turbulence is discussed. The process of the renormalization is shown and the turbulent Prandtl number is introduced. Nonlinear destabilization by the electron momentum diffusion is explained. The nonlinear eigenmode equation is derived for the dressed-test-mode for the inhomogeneous plasma in the shear magnetic field. The eigenvalue equation is solved, and the least stable mode determines the anomalous transport coefficient. Formula of thermal conductivity is presented for the system of bad average magnetic curvature (current diffusive interchange mode (CDIM) turbulence) and that for the average good magnetic curvature (current diffusive ballooning mode (CDBM) turbulence). The transport coefficient, scale length of fluctuations and fluctuation level are shown to be the increasing function of the pressure gradient. Verification by use of the nonlinear simulation is shown. The bifurcation of the electric field and improved confinement is addressed, in order to explain the H-mode physics. Improved confinement and the dynamics such as ELMS are explained. Application to the transport analysis of tokanraks is also presented, including the explanations of the L-mode confinement, internal transport barrier as well as the role of current profile control.

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