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Author(s):
K. Yamazaki and T. Amano
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Title:
Plasma Transport Simulation Modeling for Helical Confinement Systems
Date of publication:
Aug. 1991
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Key words:
equilibrium-transport simulation, neoclassical transport, anomalous transport, drift wave turbulence, empirical transport scaling, LHD(Large Helical Device), CHS(Compact Helical System)
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Abstract:
New empirical and theoretical transport models for helical confinement systems are developed based on the neoclassical transport theory including the effect of radial electric field and multi-helicity magnetic components, and the drift wave turbulence transport for electrostatic and electromagnetic modes, or the anomalous semi-empirical transport. These electron thermal diffusivities are compared with CHS (Compact Helical System) experimental data, which indicates that the central transport coefficient of the ECH plasma agrees with the neoclassical axi-symmetric value and the transport outside the half radius is anomalous. On the other hand, the transport of NBI-heated plasmas is anomalous in the whole plasma region. This anomaly is not explained by the electrostatic drift wave turbulence models in these flat-density-profile discharges. For the detailed prediction of plasma parameters in LHD (Large Helical Device), 3-D (dimensional) equilibrium /1-D transport simulations including empirical or drift wave turbulence models are carried out, which suggests that the global confinement time of LHD is determined mainly by the electron anomalous transport near the plasma edge region rather than the helical ripple transport in the core region. Even if the ripple loss can be eliminated, the increase of the global confinement is 10 %. However, the rise in the central ion temperature is more than 20 %. If the anomalous loss can be reduced to the half level of the present scaling, Iike so-called "H-mode" of the tokamak discharges, the neoclassical ripple loss through the ion channel becomes important even in the plasma core. The 5 % radial inward shift of the plasma column with respect to the major radius is effective for improving plasma confinement and raising more than 50 % of the fusion product by reducing this neoclassical asymmetric ion transport loss and increasing 10 % in the plasma radius.
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