  The accumulation of impurities in the core of magnetically confined plasmas,
resulting from standard collisional transport mechanisms, is a known threat to
their performance as fusion energy sources. Whilst the axisymmetric tokamak
systems have been shown to benefit from the effect of temperature screening,
that is an outward flux of impurities driven by the temperature gradient,
impurity accumulation in stellarators was thought to be inevitable, driven
robustly by the inward pointing electric field characteristic of hot fusion
plasmas. We have shown in Helander et. al. (2017b) that such screening can in
principle also appear in stellarators, in the experimentally relevant mixed
collisionality regime, where a highly collisional impurity species is present
in a low collisionality bulk plasma. Details of the analytic calculation are
presented here, along with the effect of the impurity on the bulk ion flow,
which will ultimately affect the bulk contribution to the bootstrap current.
