Influence of the normalised gyroradius on neoclassical transport in global gyrokinetic simulations using the code GT5D

Obrejan, K.; Idomura, Yasuhiro   ; Honda, Mitsuru*

The use of tungsten in plasma facing components inevitably leads to the pollution of the fusion plasma by heavy impurities and their accumulation at the core. Although heavy impurity transport has been estimated by the neoclassical transport theory, recent studies exhibited differences between global gyrokinetic simulations and the Hirshman-Sigmar (HS) moment approach, a commonly employed local theory. We performed a thorough benchmark for neoclassical particle transport of various impurities using the newly upgraded multi-species linear Fokker-Plank collision operator of our gyrokinetic full-f Eulerian simulation code GT5D. While good agreement was obtained in the case of flat temperature profiles, the dependence on the temperature gradient was found to be much weaker than the H-S theory in small machine sizes. Good agreement between GT5D and the H-S theory was recovered only for the case of large machine sizes, similar to ITER but beyond that of most current fusion devices.