Physics and engineering design of the divertor scraper element for the W7-X stellarator

A new high-heat-flux divertor component for the Wendelstein 7-X (W7-X) stellarator, the scraper element (SE), is being designed to protect overloaded areas of the primary divertor module during the bootstrap current evolution in certain operational scenarios. The SE will be constructed from water-cooled carbon fiber reinforced composite monoblocks capable of handling a steady-state heat load of 20MW/m². The SE will intercept magnetic field lines and associated plasma fluxes that would carry heat to the overloaded areas, and is expected to receive a peak flux of approximately 16MW/m² for ~10 seconds. The design procedure, incorporating constraints imposed by plasma physics and engineering considerations, and the current status of the SE design is presented.