Comparison of toroidal rotation velocities of different impurity ions in the DIII-D tokamak

Measurements of the relative toroidal rotation velocities of low Z impurity ions have been made in DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)] plasmas that have a strong core pressure gradient and reduced anomalous transport. They show that the differences in toroidal rotation velocities agree with predictions of neoclassical transport theory. The toroidal rotation velocities are measured via charge exchange recombination (CER) spectroscopy of the impurity species. Taking into account the non-negligible effect of energy dependent charge exchange cross sections, quantitative agreement is found between the measured and predicted difference in toroidal rotation velocities, including the strong Z dependence. The predicted difference between the measured impurity rotation velocity and the main ion rotation velocity can be substantial and therefore care should be taken in using quantitative results from impurity rotation measurements and applying them to the bulk plasma