Non-local Simulation of the Formation of Neoclassical Ambipolar Electric Field in Non-axisymmetric Configurations

Neoclassical transport simulation code (FORTEC-3D) applicable to non-axisymmetric configurations is developed. Adoption of a new hybrid simulation model, in which ion transport is solved by using the delta f Monte-Carlo method including the finite-orbit-width effects while electron transport is solved by a reduced ripple-averaged kinetic equation, makes it possible to simulate the dynamism of non-local transport phenomena with self-consistently developing radial electric field within a allowable computation time. Time evolution of radial electric field in LHD plasma is simulated in the full volume of confinement region, and the finite-orbit-width effect of neoclassical transport is found to make the negative ambipolar electric field more larger than the prediction by a local transport theory

Electromagnetic gyrokinetic turbulence in finite-beta helical plasmas

A saturation mechanism for microturbulence in a regime of weak zonal flow generation isinvestigated by means of electromagnetic gyrokinetic simulations. The study identifies a newsaturation process of the kinetic ballooning mode (KBM) turbulence originating from the spatial structure of the KBM instabilities in a finite-beta Large Helical Device (LHD) plasma.Specifically, the most unstable KBM in LHD has an inclined mode structure with respect to the mid-plane of a torus, i.e., it has a finite radial wave-number in flux tube coordinates, in contrast to KBMs in tokamaks as well as ion-temperature gradient modes in tokamaks and helical systems. The simulations reveal that the growth of KBMs in LHD is saturated by nonlinear interactions of oppositely inclined convection cells through mutual shearing as well as by the zonal flow. The saturation mechanism is quantitatively investigated by analysis of the nonlinear entropy transfer that shows not only the mutual shearing but also a self-interaction with an elongated mode structure along the magnetic field line