Radiation behaviour in ASDEX divertor discharges at the density limit

The radiation behaviour close to the density limit (DL) of ohmically and NI-heated D2 discharges in the old and the new ASDEX divertor configuration, with uncoated and with boronized vessel walls, is investigated. At qa > 3, the DL is usually preceded by a Marfe. At the onset of the Marfe, the Marfe limit (MaL), main chamber radiation RAD is about 40% of the heating power and divertor radiation DIV is about 20%. During the Marfe, RAD reaches 70% and DIV falls to about 10%. With boronized walls and only at very high qa (qa∝6.0), the Marfe can become quasi-stationary. The DL is influenced but not caused by radiation. At qa<2.6, the DL is presumably connected with MHD instabilities. A frequently observed DL minimum at qa=2.1 is not due to radiation. (orig.)