Ultra Long Turbulent Eddies, Magnetic Topology, and the Triggering of Internal Transport Barriers in Tokamaks

TL;DR

This paper shows that ultra long turbulent eddies aligned with magnetic field lines in tokamaks can significantly reduce heat transport, offering new strategies for improving plasma confinement and explaining observed internal transport barriers.

Contribution

It introduces the concept of ultra long eddies extending along magnetic field lines and demonstrates their impact on heat transport reduction in tokamak plasmas.

Findings

Ultra long eddies can extend hundreds of poloidal turns.

Such eddies can dramatically reduce heat transport.

Modeling different magnetic topologies reveals new confinement strategies.

Abstract

Local nonlinear gyrokinetic simulations of tokamak plasmas demonstrate that turbulent eddies can extend along magnetic field lines for hundreds of poloidal turns when the magnetic shear is very small. By accurately modeling different field line topologies (e.g. low-order, almost rational, or irrational safety factor), we show that the parallel self-interaction of such "ultra long" eddies can dramatically reduce heat transport. This reveals novel strategies to improve confinement, constitutes experimentally testable predictions, and illuminates past observations of internal transport barriers.