Dependence of intrinsic rotation reversals on collisionality in MAST

TL;DR

This study investigates how collisionality influences intrinsic rotation reversals in MAST tokamak plasmas, combining experimental observations with a novel 1D model that accurately predicts rotation sign changes based on plasma profiles.

Contribution

The paper introduces a new 1D model linking collisionality to intrinsic rotation reversals, validated against experimental data from MAST.

Findings

Intrinsic rotation reversals observed in spherical tokamak MAST.

The 1D model accurately predicts rotation sign changes.

Collisionality significantly affects radial angular momentum transport.

Abstract

Tokamak plasmas rotate even without external injection of momentum. A Doppler backscattering system installed at MAST has allowed this intrinsic rotation to be studied in Ohmic L-mode and H-mode plasmas, including the first observation of intrinsic rotation reversals in a spherical tokamak. Experimental results are compared to a novel 1D model, which captures the collisionality dependence of the radial transport of toroidal angular momentum due to the effect of neoclassical flows on turbulent fluctuations. The model is able to accurately reproduce the change in sign of core toroidal rotation, using experimental density and temperature profiles from shots with rotation reversals as inputs and no free parameters fit to experimental data.