Global effects on the variation of ion density and electrostatic potential on the flux surface in helical plasmas

Since the observation of impurity hole in LHD, which contradicts the prediction of the conventional neoclassical transport theory, several attempts have been made to explain the mechanism behind the phenomenon. Consideration of the impact of electrostatic potential variation within the flux surface, Φ₁, is one of those attempts. However, all of the numerical studies that have investigated the effect of Φ₁ to date have been conducted with local simulation codes, and no global calculation has been performed yet. Here, a global neoclassical simulation code FORTEC-3D is applied to evaluate Φ₁, including the global effects, for the first time. The global simulation result for a high-temperature low-density plasma, which corresponds to an impurity hole plasma, shows significant difference from the local simulation results in the Φ₁ profile. This indicates that consideration of the global effects is essential for quantitative evaluation of impurity neoclassical transport in an impurity hole plasma. (author)