Interaction between neoclassical effects and ion temperature gradient turbulence in gradient- and flux-driven gyrokinetic simulations

Abstract

Neoclassical and turbulent transport in tokamaks have been studied extensively over the past decades, but their possible interaction remains largely an open question. The two are only truly independent if the length scales governing each of them are sufficiently separate, i.e. if the ratio ρ * between ion gyroradius and the pressure gradient scale length is small. This is not the case in particularly interesting regions such as transport barriers. Global simulations of collisional ion-temperature-gradient-driven microturbulence performed with the nonlinear global gyrokinetic code Gene are presented. In particular, comparisons are made between systems with and without neoclassical effects. In fixed-gradient simulations the modified radial electric field is shown to alter the zonal flow pattern such that a significant increase in turbulent transport is observed for ρ * 1/300. Furthermore, the dependency of the flux on the collisionality changes. In simulations with fixed power input we find that the presence of neoclassical effects decreases the frequency and amplitude of intermittent turbulent transport bursts (avalanches) and thus plays an important role for the self-organisation behaviour.

Global electromagnetic turbulence simulations of W7-X-like plasmas with GENE-3D

“…At the current stage, GENE-3D uses a linearised Landau-Boltzmann collision operator for C[F 1,σ ]. Furthermore, the interplay between neoclassical and gyrokinetic physics is represented by the term coupling the curvature and ∇B drifts to the background Maxwellian (Oberparleiter et al 2016), and the effects of a long-wavelength, radial electric field on the system (Helander & Simakov 2008;Mishchenko & Kleiber 2012) are represented by the term proportional to v E 0 in (2.3). Though they are incorporated in the main algorithm, these effects are neglected in the simulations presented in this paper for simplicity.…”

Self-consistent gyrokinetic modeling of neoclassical and turbulent impurity transport

“…Previous evidences of such a synergy have been reported in the literature. They deal with poloidal flow [51], heat transport [53,54] and parallel momentum transport [36,55]. Also, drift wave turbulence has been shown analytically to be able to significantly contribute to the bootstrap current through direct modification of the axisymmetric plasma current distribution via turbulence-induced electron detrapping [56].…”

Comparative collisionless alpha particle confinement in stellarator reactors with the XGC gyrokinetic code

“…It has been shown that flux tube simulations of core microturbulence are therefore insufficient, and a flux surface global approach is necessary 2 . Furthermore, it has been shown that neoclassical transport and microturbulence undergo multiscale interactions in toroidal magnetic fusion devices generally [3][4][5] . Since microturbulent transport should dominate in at least the edge and outer core of an optimised stellarator, while neoclassical transport should continue to dominate in the inner core 6 , this is likely to be especially so in optimised stellarators and a radially global model is also likely needed.…”