Spectroscopic study of edge poloidal rotation and radial electric fields in the DIII-D tokamak (invited)

Doppler-shift spectroscopy has shown that finite values of poloidal rotation velocity vθ and of radial electric field Er exist at the edge of a tokamak plasma and that dramatic increases occur in these parameters at an L-H transition. Er is negative in the L mode and becomes more negative in the H mode; vθ increases in magnitude at the transition. In addition, the radial gradients (shear) of vθ and Er are large and these gradients also increase at the L-H transition. These results are based on measurements of Doppler shifts of light emitted by He II ions, located in a region about 1–3 cm inside the separatrix. These observations have been made with horizontally viewing and vertically viewing spectrometer systems on the DIII-D tokamak. The nearly orthogonal views of these systems are used to determine the plasma’s flow velocity in terms of the orthogonal sets vθ and vφ or of v⊥ and v∥. Knowledge of v⊥ is used to calculate Er from the force balance equation for a single ion species. The existing results impose constraints on theories of the L-H transition. More detailed studies of the spatial profiles and temporal evolution of vθ and Er will be made with upgraded instrumentation, which is now coming on-line.