  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.
