P. Junghanns

Design and test of the support elements of the W7-X superconducting magnets

The Wendelstein 7-X stellarator is presently under construction at the Max-Planck-Institute for Plasma Physics in Greifswald with the goal to verify that a stellarator magnetic confinement concept is a viable option for a fusion power plant. The superconducting magnet system has to fulfill demanding requirements regarding magnetic field, loads, manufacturing and assembly. The magnet support system consists of several types of structural components. The main one is the central support structure (CSS) to which the superconducting coils are connected through Central Support Elements (CSE). These are bolted interfaces that allow for flange opening to reduce loads on the components. The non-planar coils (NPC) are toroidially interconnected via lateral support elements (LSE) and narrow support elements (NSE). NSE are contact supports consisting of Al bronze pads that allow for sliding under large compressive loads between the coils. The planar coils (PC) are connected to the NPC through planar support elements (PSE). At the module and half-module separation planes Contact Elements (CTE) connect the neighbouring NPC. An integrated programme of design, FE analysis, experiments and assembly trials has been undertaken. The NSE experimental program provided confidence that the pads can cope with the requirements regarding loads and cycles. Weld trials provided procedures for installing the LSE whilst keeping shrinkage and distortion within tight limits. Tests have been carried out to provide insight on the functioning of the CSE, in particular of the bolts and high performance Superboltreg-nuts during pre-load. This paper gives an overview of the integrated program on the W7-X support elements.

Wendelstein 7-X high heat flux components

The actively water-cooled In-Vessel Components (IVCs) of the stellarator Wendelstein 7-X consist of the divertor, the first wall protection components, the port liners, each designed for different loading conditions, and the associated pipework, the control coils, the cryo-pump system, the Glow discharge electrodes, and a set of diagnostics. The divertor, designed for high heat fluxes, is a set of 10 target and baffle units arranged along the plasma surface. The design and production of these high heat flux (HHF) components is a challenging task. The divertor target elements, which are based on flat CFC (carbon-carbon fibre composite) tiles bonded via active metal casting onto CuCrZr cooling structures required intensive development and testing to reach a reliable performance; removing, under stationary conditions, 10 MW/m2. Industrially manufactured high quality target elements have been delivered and assessed, and the process of incorporating them into assembly units, so-called modules, has begun. The time scale for the completion of the HHF divertor has been held for the last four years and the final delivery of the HHF divertor is still planned in 2017. In parallel to the realization of the divertor the remaining IVCs have been defined, developed, designed and fabricated and the installation of many of these components has begun. Some of these components can also be expected, for a short period of time, to receive high heat loads approaching those of the divertor. These components will be described, in detail, from conception to realization.

Design of Narrow Support Elements for Non Planar Coils of Wendelstein 7-X

The stellarator Wendelstein 7-X is presently under construction and assembly in Greifswald, Germany. One of the main structural elements which have to take the electromagnetic forces of the superconducting coil system are the narrow support elements (NSE). They are placed between the non planar coils and have to take very high compressive forces while relative sliding and tilting of the coils must be allowed. The design has been optimised with regard to a proper load distribution among all support elements taking also into account manufacturing and assembly tolerances. The paper describes the design, analysis and tests which have been carried out for the NSEs

Status of High Heat Flux Components at W7-X

The actively water-cooled in-vessel components (IVCs) of the stellarator Wendelstein 7-X consist of the divertor, the first wall protection components, the port liners, each designed for different loading conditions, and the associated pipework, the control coils, the cryo-pump system, the Glow discharge electrodes, and a set of diagnostics. The divertor, designed for high heat fluxes (HHFs), is a set of 10 target and baffle units arranged along the plasma surface. The design and production of these HHF components is a challenging task. The divertor target elements, which are based on flat carbon-carbon fiber composite tiles bonded via active metal casting onto CuCrZr cooling structures required intensive development and testing to reach a reliable performance; removing, under stationary conditions, 10 MW/m2. Industrially manufactured high quality target elements have been delivered and assessed, and the process of incorporating them into assembly units, so-called modules, has begun. The time scale for the completion of the HHF divertor has been held for the last four years and the final delivery of the HHF divertor is still planned in 2017. In parallel to the realization of the divertor, most of the remaining IVCs have been defined, developed, designed, and fabricated and the installation of many of these components has begun. Some of these components can also be expected, for a short period of time, to receive high heat loads approaching those of the divertor. These components will be described, in detail, from conception to realization.

Design and Test of Wendelstein 7-X Water-Cooled Divertor Scraper

Heat load calculations have indicated the possible overloading of the ends of the water-cooled divertor facing the pumping gap beyond their technological limit. The intention of the scraper is the interception of some of the plasma fluxes both upstream and downstream before they reach the divertor surface. The scraper is divided into six modules of four plasma facing components (PFCs); each module has four PFCs hydraulically connected in series by two water boxes (inlet and outlet). A full-scale prototype of one module has been manufactured. Development activities have been carried out to connect the water boxes to the cooling pipes of the PFCs by tungsten inert gas internal orbital welding. This prototype was successfully tested in the GLADIS facility with 17 MW/m2 for 500 cycles. The results of these activities have confirmed the possible technological basis for a fabrication of the water-cooled scraper.