Transport-driven toroidal rotation in the tokamak edge

TL;DR

This paper demonstrates that ion drift orbit interactions with diffusive radial transport can spontaneously generate significant toroidal rotation in tokamak edges, with rotation scaling and X-point effects aligning with experimental observations.

Contribution

It introduces a novel mechanism linking passing-ion drift orbits and residual stress to intrinsic toroidal rotation in tokamak edges.

Findings

Rotation scales with ion temperature over poloidal magnetic field strength.

Inboard X-point enhances co-current rotation.

Outboard X-point enhances counter-current rotation.

Abstract

The interaction of passing-ion drift orbits with spatially-inhomogeneous but purely diffusive radial transport is demonstrated to cause spontaneous toroidal spin-up to experimentally-relevant values in the tokamak edge. Physically, major-radial orbit shifts cause orbit-averaged diffusivities to depend on parallel velocity, including its sign, leading to residual stress. The resulting intrinsic rotation scales with ion temperature over poloidal magnetic field strength, resembling typical experimental scalings. Additionally, an inboard (outboard) X-point is expected to enhance co- (counter-) current rotation.