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Author(s):
K. Itoh, S.-I. Itoh, A. Fukuyama, H. Sanuki, K. Ichiguchi and J. Todoroki
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Title:
Improved Models of beta-Limit, Anomalous Transport and Radial Electric Field with Loss Cone Loss in Heliotron / Torsatron
Date of publication:
Sep. 1992
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Key words:
IAEA, fusion energy conference, Wurzburg
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Abstract:
Theoretical study is made on the physics mechanisms which determine the beta-limit, the anomalous transport, and the radial electric field and loss cone. New theory is developed to analyze the stability boundary against the interchange mode in high-aspect-ratio toroidal helical plasmas, taking into account the transport processes. The stability beta-1imit is given at finite beta-value, and the dependences on the plasma parameters and on the transport coefficient are investigated. It is found that the current-diffusive interchange mode is more important than the resistive mode in hot plasmas. The beta-limit is predicted in the range of experimental observation for the anomalous transport. The dynamics of the pressure gradient and mode amplitude around this stability boundary are analysed. As the heating power is increased, the dynamics changes from the monotonous saturation, through the saturation with overshoot, and to the sawtoothing. Using the mean-field theory approach of statistical physics for the microscopic current-diffusive interchange mode, the anomalous transport theory is developed. The expression of the thermal transport coefficient is obtained. The pressure gradient, not the temperature itself, enhances the transport coefficient. Comparison with experimental observations from various aspects is made, and the model explains experimental observations. The method to obtain the self-consistent picture of the radial electric field E_r and the loss cone loss is explored. The structure of E_r and the loss cone are obtained, and it is confirmed that the direct ion loss makes E_r neat edge more negative. Effects of other nonclassical loss are also evaluated.
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