AIP Digital Archive
The role of impurity dynamics in resistivity-gradient-driven turbulence is investigated in the context of modeling tokamak edge plasma phenomena. The effects of impurity concentration fluctuations and gradients on the linear behavior of rippling instabilities and on the nonlinear evolution and saturation of resistivity-gradient-driven turbulence are studied both analytically and computationally. At saturation, fluctuation levels and particle and thermal diffusivities are calculated. In particular, the mean-square turbulent radial velocity is given by 〈vˆ2r〉 =(E0Ls/Bz)2 (L−1η+L−1z)2. Thus edged peaked impurity concentrations tend to enhance the turbulence, while axially peaked concentrations tend to quench it. The theoretical predictions are in semiquantitative agreement with experimental results from the TEXT [Bull. Am. Phys. Soc. 30, 1443 (1985)], Caltech [Phys. Fluids 29, 309 (1986)], and Tosca [in the Proceedings of the 12th European Conference on Controlled Fusion and Plasma Physics (European Physical Society, Budapest, 1985), Vol. I, p. 311] tokamaks. Finally, a theory of the density clamp observed during CO-NBI on the ISX-B tokamak [in Plasma Physics and Controlled Nuclear Fusion Research (IAEA, Vienna, 1981), Vol. I, p. 377] is proposed.
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