Up-down symmetry of the turbulent transport of toroidal angular momentum in tokamaks

TL;DR

This paper demonstrates that in tokamaks, the turbulent transport of toroidal angular momentum exhibits specific symmetries under up-down reflection and sign changes in rotation, impacting models of spontaneous rotation.

Contribution

It identifies two symmetries in the gyrokinetic equations that determine the behavior of momentum transport in tokamaks.

Findings

Transport changes sign under up-down reflection and rotation sign change

Transport vanishes in symmetric tokamaks without rotation or shear

Implications for modeling spontaneous rotation in tokamaks

Abstract

Two symmetries of the local nonlinear delta-f gyrokinetic system of equations in tokamaks in the high flow regime are presented. The turbulent transport of toroidal angular momentum changes sign under an up-down reflection of the tokamak and a sign change of both the rotation and the rotation shear. Thus, the turbulent transport of toroidal angular momentum must vanish for up-down symmetric tokamaks in the absence of both rotation and rotation shear. This has important implications for the modeling of spontaneous rotation.