Global kinetic simulation studies on the collisionality dependency of the neoclassical toroidal viscosity driven by perturbed magnetic field

Matsuoka, Seikichi ; Idomura, Yasuhiro   ; Satake, Shinsuke*

Effects of non-axisymmetric magnetic field perturbations on plasma transport in tokamaks have attracted much attention from the view point of the control of the plasma performance and instabilities. Recent studies pointed out that there exists qualitative discrepancy in predicting the collisional viscosity driven by the perturbation between a theoretical bounce-averaged model and a global kinetic simulation. Clarifying the cause of the discrepancy is a key issue to establish a reliable basis for the NTV predictions. In this work, we perform two types of global kinetic simulations for the NTV to investigate the discrepancy from the theoretical model. As a result, it is first demonstrated that the discrepancy arises owing to the following two mechanisms; (1) resonant structures predicted in the bounce-averaged model become weak due to global particle orbit width effects, and (2) the velocity space structures are damped by the phase mixing.