Comparison of measured and simulated heat and particle fluxes during high-beta mimic experiments on the W7-X stellarator

Heat and particle fluxes to the Wendelstein 7-X (W7-X) divertor are compared to 3D simulations for a set of magnetic configurations designed to mimic the evolution of plasma currents in future high-beta plasmas which have been predicted to result in overloaded components. The experiments were performed in the first diverted operational phase of W7-X (OP1.2a) before the installation of divertor “scraper elements” which are designed to intercept the flux to the otherwise overloaded components. Comparison of heat fluxes from the OP1.2a experiments indicates that the patterns and relative magnitudes can be well reproduced with fluid transport simulations using EMC3-EIRENE, as well as simple field line diffusion models. These results indicate that the approach of mimicking otherwise inaccessible high-beta conditions using vacuum magnetic configurations is valid and increase confidence that scraper elements will protect the overloaded components as designed. The scraper elements have the disadvantage of intercepting flux in steady state OP2 configurations, reducing pumping efficiency and affecting particle transport. This effect is investigated using filtered cameras and spectroscopy. Initial results from experiments with two scraper elements installed (OP1.2b) will also be presented.