Scrape-off layer model for the study of impurity retention in the pumped divertor planned for JET

The paper presents a model of the plasma boundary region that has been developed to study the flow of impurities generated at the target plates in the pumped divertor configuration planned for JET. For the flow equations the model is one-dimensional, parallel to the magnetic field, but the neutral species is treated in two dimensions. All ionization stages of an impurity can be treated separately or, alternatively, an average charge impurity species can be considered. The validity of this approximation is assessed. The presented results show that impurities can be retained near the target plates by a forced flow of plasma generated by recirculating, across the separatrix from the main plasma to the scrape-off layer, a fraction of the flow reaching the target plates.