Impurity transport in detached plasmas

Transport of metallic impurities in the plasma edge was compared for normal and detached Tokamak plasmas. A neo-classical model, valid for a dirty plasma in the Pfirsch-Schluter regime, was used to calculate the impurity flux terms. Changes in the edge density and temperature profiles, characteristic of detached discharges, were seen to greatly influence the impurity transport. In particular, the inward convective velocity increased significantly because of the detachment. A one-dimensional transport code was used to evaluate the influence of the edge transport modifications on the global impurity confinement time. Code predictions are in qualitative agreement with experimental measurements made on TEXTOR. (author)