Impurity transport in tokamak plasmas containing momentum sources

Impurity transport in a tokamak plasma in the presence of an externally imposed momentum source is considered. Including a model collision term to damp toroidal angular momentum and imposing the conventional ambipolar transport condition, the authors obtain expressions demonstrating that properly chosen momentum sources (e.g. radio-frequency fields) can cause outward the impurity transport. Estimates of the RF source strength needed to stop inward impurity diffusion show that the power absorbed by the plasma is small.