Dependence of intrinsic rotation reversals on collisionality in MAST

摘要

Tokamak plasmas rotate even without external injection of momentum. A Dopplerbackscattering system installed at MAST has allowed this intrinsic rotation tobe studied in Ohmic L-mode and H-mode plasmas, including the first observationof intrinsic rotation reversals in a spherical tokamak. Experimental resultsare compared to a novel 1D model, which captures the collisionality dependenceof the radial transport of toroidal angular momentum due to the effect ofneoclassical flows on turbulent fluctuations. The model is able to accuratelyreproduce the change in sign of core toroidal rotation, using experimentaldensity and temperature profiles from shots with rotation reversals as inputsand no free parameters fit to experimental data.