Edge rotation from momentum transport by neutrals

TL;DR

This paper models how neutral atoms influence plasma momentum transport and intrinsic rotation through charge-exchange processes, considering various plasma geometries and impurity effects.

Contribution

It introduces a coupled neutral-ion model to predict intrinsic plasma rotation self-consistently, accounting for arbitrary collisionality and geometric factors.

Findings

Neutral atoms significantly affect plasma momentum transport.

The model predicts intrinsic rotation profiles in different geometries.

Impurity rotation can be analyzed using the same framework.

Abstract

Due to their high cross field mobility, neutral atoms can have a strong effect on transport even at the low relative densities found inside the separatrix. We use a charge-exchange dominated model for the neutrals, coupled to neoclassical ions, to calculate momentum transport when it is dominated by the neutrals. We can then calculate self-consistently the radial electric field and predict the intrinsic rotation in an otherwise torque-free plasma. Using a numerical solver for the ion distribution to allow arbitrary collisionality, we investigate the effects of inverse aspect ratio and elongation on plasma rotation. We also calculate the rotation of a trace carbon impurity, to facilitate future comparison to experiments using charge exchange recombination spectroscopy diagnostics.