Investigation of the impact of flux expansion on tungsten content and radiation in JET-ILW

Abstract

© 2020 The Authors The present paper shows the results of the investigation about the effects of the flux-expansion variation at the inner strike point location on the tungsten content in the plasma core, and on the bulk radiation in JET-ILW. The divertor geometries have been designed using the plasma equilibrium code CREATE-NL. The designed divertor geometries were experimentally achieved via a suitable optimization of the divertor coils current on a few discharges with similar additional heating. Diagnostics were used to examine: the tungsten source from the divertor tiles in both inter-ELM and intra-ELM phases, the tungsten content and profile shape inside the plasma core, and the total radiation. Preliminary results suggest that there is not a strong impact of the flux expansion on the tungsten erosion at the strike point. A discharge with high flux compression shows nonetheless a slight increase in core tungsten concentration but this might also be the result of changes in ELMs frequency due to flux expansion variation. The effect on ELMs dynamic has been clearly observed making more difficult the present analysis and should be further studied in future experiments. Edge analysis performed with the SOLEDGE2D code seems to exclude a significant variation of edge transport with flux expansion, pointing to an indirect effect on pumping efficiency and consequently on edge density.