Turbulent momentum transport due to neoclassical flows

TL;DR

This paper investigates how neoclassical flow effects influence turbulent momentum transport in tokamaks, revealing how different contributions vary with collisionality through gyrokinetic simulations.

Contribution

It categorizes neoclassical effects on turbulent momentum transport and evaluates their relative importance across collisionality regimes using gyrokinetic simulations.

Findings

At low collisionality, particle and parallel flows dominate.

At moderate collisionality, poloidal electric fields and density/temperature gradients become significant.

The importance of neoclassical effects varies with collisionality.

Abstract

Intrinsic toroidal rotation in a tokamak can be driven by turbulent momentum transport due to neoclassical flow effects breaking a symmetry of turbulence. In this paper we categorize the contributions due to neoclassical effects to the turbulent momentum transport, and evaluate each contribution using gyrokinetic simulations. We find that the relative importance of each contribution changes with collisionality. For low collisionality, the dominant contributions come from neoclassical particle and parallel flows. For moderate collisionality, there are non- negligible contributions due to neoclassical poloidal electric field and poloidal gradients of density and temperature, which are not important for low collisionality.