New understanding of poloidal rotation measurements in a tokamak plasma

Significant atomic physics corrections to the measured poloidal velocity using charge exchange spectroscopy have been neglected when interpreting impurity poloidal velocity. In the presence of a magnetic field, the gyro motion of the impurity ion along with the finite lifetime of the observed state results in an additional line shift that scales with ion temperature and magnetic field strength. Effects of collisions on the lifetime of excited states, cascades from higher longer-lived n levels, and charge exchange from excited beam neutrals are calculated to determine necessary corrections to the measured poloidal velocity. The accuracy of computed corrections is tested utilizing symmetric upward and downward views from the TFTR poloidal rotation diagnostic.