Observation of poloidal asymmetry in impurity-ion emission due to del B drifts

Poloidally asymmetric impurity-ion emission has been observed in high-density discharges of the Alcator Tokamak. The sense of the asymmetry reverses when the direction of the toroidal field is reversed, and all observed dependences of the strength of the asymmetry upon proton density and safety factor are consistent with the explanation that the gradient and curvature drifts of the highly collisional impurity ions cause the asymmetry. Thus the asymmetry implies that the drift is a major impurity transport process at high densities