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The results of divertor studies on ASDEX Upgrade, at currents of up to 1.2 MA and heating powers up to 10 M W are described, with emphasis on the ELMy H-mode. The spatial and temporal characteristics of their heat load, and the simulation of ELMs by a time-dependent scrape-off layer code are described. High gas puff rata were found to lead to a large increase in divertor neutral pressure, at modest changes in %, and to a strong reduction in timeaveraged power flow and complete detachment from both target plates in between ELMs. Using pre-programmed puffs of neon and argon, the radiative power losses could be raised to 75% of the heating power, in H-regime discharges, and the regime of enhanced divertor neutral pressure was found also to lead to an improved pumping of recycling impurities. 1.Introduction:ASDEX Upgrade is a mid-size tokamak w i t h non-circular cross-section (major radius R, , = 1.625m, horizontal minor radius a = 0.5 m, elongation b/a = 1.6), purpose-designed as a poloidal divertor device (Figure 1). Further distinguishing features of it are the poloidal field coils placed outside the toroidal ones, and the presence of a saddle coil ("PSL" .. pssive Stabilising loop) inside the vacuum vessel for stabilising the vertical displacement instability. Together, these two features provide a relatively large space between the vacuum vessel and the X-point of the poloidal field lines, although the present divertor configuration, selected to optimise the heat load distribution, places the target plates relatively close to the x-point.

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The completely detached high confinement (CDH) regime established recently in high power ASDEX-Upgrade single null divertor discharges is described. The standard CDH mode scenario with feedback controlled external deuterium and neon puffing is analysedin detail with respect to its divertor detachment and confinement properties. Impurity transport and pumping effects and the density operation window of the CDH mode are outlined. First results with other impurity radiators (N, Ar) are given.Finally the CDH mode operation space is discussed in terms of main chamber and scrapeoff layer plus divertor radiation and possible consequences for future fusion experiments are outlined.