Impurities in fusion plasmas lead to a loss of reactivity by radiation and fuel dilution. 1 The impurity concentration in the plasma is determined both by the production rate and transport in the plasma, particularly the transport in the boundary layer. 1'2 In this layer impurities, usually starting as cold atoms or molecules, are ionised and heated while diffusing both parallel and perpendicularly to the confining magnetic field. Atomic physics plays an important role in these processes. In the present paper we consider some of the experimental results on impurity behaviour in this boundary and some simple models to describe their behaviour. The discussion will be on the behaviour of impurities in plasmas bounded by limiters.
