The processes by which impurities are produced and enter the discharge are discussed. Emphasisis placed on sputtering at the limiter and an analytical global model is described whichincorporates the self-stabilizing effects which control the edge temperature. Predictions ofthe scaling of edge temperature and of total radiated power are compared with experimental datafrom JET and other tokamaks operating with limiters. Under many conditions the scaling of theedge conditions and of the radiated power is accurately predicted. Impurity transport in theboundary and the question of how to control the boundary layer is then discussed. The exampleof the Impurity Control Limiter on DITE is described.
Investigations of impurity control in JET using fuelling, and interpretation of experiments using the LIM impurity code