Determination of radial electric field from Pfirsch-Schluter flows in a stellarator

Inboard/outboard asymmetry in the impurity ion parallel flows is measured in the HSX stellarator using Charge Exchange Recombination Spectroscopy (CHERS). This observation is consistent with the Pfirsch-Schluter flows predicted by neoclassical theory. The asymmetry of the flow is used to calculate the magnitude and direction of the radial electric field (E\textunderscore r), as well as the mean flow, using computed magnetic geometry factors. This method enables measurement of E\textunderscore r near the core of the HSX plasma where the E\textunderscore r obtained from the radial force balance equation has large uncertainties due to the relatively large width of the diagnostic neutral beam and the smaller plasma radius.