Alternative Divertor Configurations in the New Upper Divertor of ASDEX Upgrade

As one of the largest projects funded by the EUROfusion consortium, ASDEX Upgrade is currently completing the installation of a pair of in-vessel coils to investigate alternative divertor configurations in a tokamak with an exceptionally high heating power in proportion to its size. The aim is to find the optimum divertor configuration for both power exhaust and removal of the He 'ash' produced in a fusion reactor, while meeting the performance and cost constraints of such a device. The three most promising configurations are the X-divertor (XD), the low-field side snowflake minus (LFS SF-) divertor and the compact radiative divertor (CRD) [Lunt et al., Phys. Rev. Lett. 2023]. The latter consists of an X-point radiator configuration with short divertor legs. All three configurations can be investigated after the hardware upgrade, which will also include a comprehensive suite of new diagnostics and a charcoal-coated cryo-pump capable of trapping helium. This will allow the predictions of both analytical models and complex scrape-off layer transport codes, such as SOLPS-ITER and EMC3-EIRENE, used to extrapolate today's results to DEMO, to be tested. Starting with an introduction to divertor physics, the expected behaviour of the alternative divertor configurations is discussed regarding their application for a future reactor, as well as the experiments required to verify these results.