Plasma rotation and structure of the radial electric field in RFX

Plasma rotation has been investigated in the reversed field pinch experiment (RFX) both by spectroscopic means and by an array of Langmuir probes. The rotation velocity at the plasma edge has been deduced from the Doppler shift of the CIII emission line. The observation of other ions characterised by different radial positions, such as BIV and CV, has allowed an estimate of the velocity shear. The results of the spectroscopic measurements are in qualitative agreement with the electric probe results. Impurity and hydrogen rotation has been modified by external means and the effects on the velocity are in agreement with the induced radial electric field changes. The experimental results are interpreted by a Monte Carlo simulation and a single-fluid model.