Pfirsch-Schlüter impurity transport in stellarators

The Pfirsch-Schlüter transport of impurities is calculated for stellarator geometry. Contrary to the tokamak case, where the only contribution to the particle flux arises from friction between different species, in a stellarator there is another source of impurity transport due to pressure anisotropy. However, the pressure anisotropy term is usually smaller than the friction term, so that the impurity particle flux is comparable to that in a tokamak. The pressure anisotropy is nonetheless important as it causes the transport to be non-ambipolar and thereby determines the radial electric field. The presence of impurities therefore affects the radial electric field in a stellarator. The heat flux is also affected qualitatively by impurities.