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arXiv · 1506.07899

Kinetic modeling of divertor heat load fluxes in the Alcator C-Mod and DIII-D tokamaks

A. Y. Pankin·T. Rafiq·A. H. Kritz·G. Y. Park·C. S. Chang·D. Brunner·R. J. Groebner·J. W. Hughes·B. LaBombard·J. L. Terry·S. Ku
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Abstract

The guiding-center kinetic neoclassical transport code, XGC0, [C.S. Chang et. al, Phys. Plasmas 11, 2649 (2004)] is used to compute the heat fluxes and the heat-load width in the outer divertor plates of Alcator C-Mod and DIII-D tokamaks. The dependence of the width of heat-load fluxes on neoclassical effects, neutral collisions and anomalous transport is investigated using the XGC0 code. The XGC0 code includes realistic X-point geometry, a neutral source model, the effects of collisions, and a diffusion model for anomalous transport. It is observed that width of the XGC0 neoclassical heat-load is approximately inversely proportional to the total plasma current $I_{\rm p}$. The scaling of the width of the divertor heat-load with plasma current is examined for an Alcator C-Mod discharge and four DIII-D discharges. The scaling of the divertor heat-load width with plasma current is found to be weaker in the Alcator C-Mod discharge compared to scaling found in the DIII-D discharges. The effect of neutral collisions on the $1/I_{\rm p}$ scaling of heat-load width is shown not to be significant. Although inclusion of poloidally uniform anomalous transport results in a deviation from the $1/I_{\rm p}$ scaling, the inclusion of the anomalous transport that is driven by ballooning-type instabilities results in recovering the neoclassical $1/I_{\rm p}$ scaling. The Bohm or Gyro-Bohm scalings of anomalous transport does not strongly affect the dependence of the heat-load width on plasma current. The inclusion of anomalous transport, in general, results in widening the width of neoclassical divertor heat-load and enhances the neoclassical heat-load fluxes on the divertor plates. Understanding heat transport in the tokamak scrape-off layer plasmas is important for strengthening the basis for predicting divertor conditions in ITER.

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A. Y. Pankin, T. Rafiq, A. H. Kritz, G. Y. Park, C. S. Chang, D. Brunner, R. J. Groebner, J. W. Hughes, B. LaBombard, J. L. Terry, S. Ku. 2015-06-25. Kinetic modeling of divertor heat load fluxes in the Alcator C-Mod and DIII-D tokamaks. https://doi.org/10.1063/1.4931050

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