Experimental confirmation of impurity convection driven by the ion-temperature gradient in toroidal plasmas

Strong, outward convection of low- Z impurity ions has been observed in DIII-D plasmas which have reduced anomalous transport, a weak density gradient, and a strong ion-temperature gradient. Comparing the measurements with theoretical predictions of collisional (neoclassical) transport indicates that the observed outward convection results from an effect known as "temperature screening." Taking into account the non-negligible effect of anomalous transport, quantitative agreement is found between the measured transport properties and the predicted values, including the strong Z dependence.