Neoclassical transport theory has long been studied by analytic approches[1,2] which use the small-orbit-width (SOW) approximation. Recently however, the finite-orbit-width (FOW) effect on the neoclassical transport has attracted attention. Especially in the region near the magnetic axis, where relatively wide "potato" particles dominate transport processes, conventional transport theory in the SOW approximation must be modified. Recently, we presented a new transport theory[3] which is suitable to treat the FOW effect of potato paricles arond the axis. In the theory, it is shown that the ion thermal conductivity χ_i becomes much lower than that is predicted from the conventional theory in the near-axis region. This fact has also been found by several tokamak experiments and Monte Carlo transport simulations using δf method[4], which correctly includes the FOW effects in the algorithm.
Here, we show a precise comparison of χ_i between our transport theory and results from the δf simulations. Since the theory is valid in the low-collisionality regime, our δf code FORTEC has been improved so that it is numerically stable even in a high temperature, wide orbit-width plasma. From this comparison, we will find a physical understanding about how the FOW effect appears on neoclassical fluxes and transport coefficients, both of which are defined in a SOW-limit point of view as q/T=-nχdT/dr.

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