A model based on analysis of the scrape-off layer and divertor region is proposed for the disruptive density limit in divertor tokamaks. A critical edge density is derived from the power balance in front of the divertor plates. A crucial element of the model is the description of recycling. The model is extensively validated against ASDEX results. Significant differences observed in ASDEX before and after hardening are described by the model as being a consequence of the modified divertor design. In both regimes the absolute value as well as the scaling of the critical density in terms of q, Bt and Pin are reproduced.
Closed divertor operation in ASDEX Upgrade and JET