Occurrence and control of X‐point radiators and marfes in ASDEX Upgrade: experimental validation of an analytic model

Cold, dense and strongly radiating plasma volumes play an important role for power exhaust and the protection of the plasma facing components in fusion devices. A recently developed analytical model [1] deals with the occurrence of such a plasma volume known as X‐point radiator (XPR) [2], where a key role is attributed to neutral deuterium fueling. Furthermore, a criterion is derived, predicting marfes [3] when the XPR becomes MHD unstable. The main results from the model are consistent with experimental observations and with results from recent SOLPS-ITER simulations [4]. The model explains why stable XPRs are more commonly observed in metal‐wall tokamaks with impurity seeding. The model provides simple expressions which can be used for the extrapolation to future devices.

This contributions gives a brief introduction into the model and the underlying physical picture. It reports on recent experimental tests of the model carried out for high-power H-mode plasma on ASDEX Upgrade. It is shown, that active XPR control, which is normally achieved by nitrogen seeding, can also be achieved by deuterium fueling. Also disruption avoidance schemes for the H-Mode density limit [5] have been studied using both the D fueling rate and the auxiliary heating power as actuators. Predictions are made for JET, ITER and DEMO and the different behavior of XPRs and marfes for different seeding gases is discussed.