Power load studies in JET and ASDEX-Upgrade with full-W divertors

For the design and operation of large fusion devices, a detailed understanding of the power exhaust processes is necessary. This paper will give an overview of the current research on divertor power load mechanisms. The results shown are obtained in JET with the ITER-like wall (ILW)and ASDEX-Upgrade with tungsten coated plasma-facing components (PFCs). The challenges of infrared thermography on an ITER-like bulk tungsten divertor are presented. For the steady-state heat load, the power fall-off length λ_q in JET-ILW is compared to an empirical scaling found in JET and the ASDEX-Upgrade with carbon PFCs. A first attempt to scale the divertor broadening S in the ASDEX-Upgrade with tungsten PFCs is shown. The edge localized mode (ELM) duration t_ELM in JET-C and JET-ILW is compared. For similar pedestal conditions (T_e,ped and n_e,ped), similar ELM durations are found in JET-C and JET-ILW. For higher n_e,ped at the same pedestal pressure p_e,ped, longer ELM durations are found in JET-ILW. The pedestal pressure p_e,ped is found to be a good qualifier for the ELM energy fluency in both JET-C and JET-ILW. Improved diagnostic capabilities reveal ELM substructures on the divertor target occurring a few milliseconds before the ELM crash. (paper)