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A new divertor configuration (DIV-IIb) has been implemented in ASDEX Upgrade. In order to accommodate a large variety of plasma shapes with bottom triangularities (delta bot) up to 0.48, the outer strikepoint region was modified and the roof baffle was lowered and diminished at its outer part in comparison with the previous divertor (DIV-II). The inner part of the divertor strikepoint module remains unchanged, but a smooth transition to the central column is provided at the divertor entrance to minimize local hydrogen recycling. An increase in power density is observed due to geometrical reasons at the outer target, whereas the divertor radiation for similar configurations and discharge conditions is unchanged. The pumping characteristics for D and He are almost retained, suggesting a large influence of the inner divertor leg, the configuration of which remains as before. Detachment in L-mode discharges fits well into a scaling deduced from JET data and earlier ASDEX Upgrade data. A significant reduction (20%) of the L�H threshold is observed compared with DIV-II. Its density dependence is weaker than in the previous DIV-II configuration and there are hints for an influence of triangularity on power threshold. Finally, clear evidence for parasitic plasma below the divertor roof baffle is found.

Additional information

Authors: NEU R, Max-Planck-Institut für Plasmaphysik, IPP-EURATOM Association, Garching (DE);FUCHS J C, Max-Planck-Institut für Plasmaphysik, IPP-EURATOM Association, Garching (DE);KALLENBACH A ET AL, Max-Planck-Institut für Plasmaphysik, IPP-EURATOM Association, Garching (DE)
Bibliographic Reference: An article published in: Nuclear Fusion 43 (October 2003) 1191-1196
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