Finite orbit width effect on the neoclassical toroidal viscosity in the superbanana-plateau regime

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 by understanding the underlying mechanism is a key issue to establish a reliable basis for the NTV predictions. In this work, we perform two different kinds of global kinetic simulations for the NTV. As a result, it is first demonstrated that the discrepancy arises owing to the following two mechanisms; (1) the effective magnitude of the perturbation becomes weak due to the finite orbit width of the global particle orbit, and (2) the velocity space structures are damped by the phase mixing along the global particle orbit.