Turbulent momentum pinch of diamagnetic flows in a tokamak

TL;DR

This paper investigates the turbulent momentum pinch in tokamaks, focusing on the difference between flows driven by electric fields and pressure gradients, revealing their impact on plasma rotation profiles.

Contribution

It introduces a calculation of the momentum pinch for diamagnetic flows, extending previous work on Coriolis-driven flows, and compares their effects on plasma rotation.

Findings

Diamagnetic flows produce a distinct momentum pinch compared to $E\times B$ flows.

Differences in pinch effects influence intrinsic rotation peaking in tokamak edges.

The study highlights the importance of flow type in momentum transport modeling.

Abstract

The ion toroidal rotation in a tokamak consists of an $E\times B$ flow due to the radial electric field and a diamagnetic flow due to the radial pressure gradient. The turbulent pinch of toroidal angular momentum due to the Coriolis force studied in previous work is only applicable to the $E\times B$ flow. In this Letter, the momentum pinch for the rotation generated by the radial pressure gradient is calculated and is compared with the Coriolis pinch. This distinction is important for subsonic flows or the flow in the pedestal where the two types of flows are similar in size and opposite in direction. In the edge, the different pinches due to the opposite rotations can result in intrinsic momentum transport that gives significant rotation peaking.