Wendelstein 7-X high heat-flux divertor scraper element

Abstract

The Wendelstein 7-X stellarator experiment is scheduled to complete construction in 2014 and begin operation in 2015. After the first operational phase, the inertially cooled test divertor unit will be replaced with an actively cooled high heat-flux divertor which will enable the device to increase its pulse length and its steady-state plasma performance. Plasma simulations show that the evolution of bootstrap current in certain plasma scenarios produce excessive heat fluxes on the divertor edge elements. It is proposed to place an additional “scraper element” in the ten divertor locations that will capture some of the plasma flux and reduce the heat load on these divertor edge elements. Each scraper element may experience a 500 kW steady-state power load, with localized heat fluxes as high as 20 MW/m2. Computational modeling has also been performed in order to model the thermal and structural integrity of the scraper element. The peak temperature in the CFC, the total pressure drop in the cooling water, and the increase in water temperature must all be examined to stay within specific design limits. Computational fluid dynamics (CFD) modeling is performed to examine the flow paths through the multiple monoblock fingers as well as the thermal transfer through the monoblock swirl tube channels. Finite element analysis is integrated into the CFD results in order to ensure the structural integrity of the component.