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The magnetic diagnostics foreseen for the Wendelstein 7-X (W7-X) stellarator are diamagnetic loops to measure the plasma energy, Rogowski coils to measure the toroidal plasma current, saddle coils to measure the Pfirsch–Schluter currents, segmented Rogowski coils (poloidal magnetic field probes) to add information on the distribution of the plasma current density, and Mirnov coils to observe magnetohydrodynamic modes. All these magnetic field sensors were designed as classical pick-up coils, after the time integration of induced signals for 1/2 hour had been successfully demonstrated. The long-pulse operation planned for W7-X causes nevertheless significant challenges to the design of these diagnostics, in particular for the components located inside the plasma vessel, which may be exposed to high levels of microwave (electron cyclotron resonance) stray radiation and thermal radiation. This article focuses on the tests and modelling performed during the development of the magnetic diagnostics and on the design solutions adopted to meet the conflicting requirements. All pick-up coils foreseen for the initial operation phase of W7-X and their signal cable sections inside the plasma vessel and the cryostat are now installed, and their electronics and data acquisition are under preparation.

The In-Vessel Components (IVC) for the Wendelstein 7-X stellarator at the Institute for Plasma-Physics (IPP), to be installed for the initial phase of operation, are nearing completion and a significant fraction of the components was delivered in 2011 and 2012. Due to the considerable amount of different components including many variants, the timely realization required a comprehensive management approach, not only covering the demanding technology and system requirements, but also coordination, planning and control issues. A variety of tools were set up to address the technical, financial and timescale challenges. The implementation of this comprehensive management approach is illustrated by the production of the water-cooling system of the IVC. Careful design and manufacture of these components is needed to fulfil the cooling function under high vacuum conditions within very restricted available space. The evolution of the complexity of these components together with changes of boundary conditions had to be managed, integrated into the overall project planning and adequately resourced.

The operation of W7-X stellarator for pulse length up to 30 min with 10 MW input power requires a full set of actively water-cooled plasma facing components. From the lower thermally loaded area of the wall protection system designed for an averaged load of 100 kW/m 2 to the higher loaded area of the divertor up to 10 MW/m 2 , various design and technological solutions have been developed meeting the high load requirements and coping with the restricted available space and the particular 3D-shaped geometry of the plasma vessel. 80 ports are dedicated alone to the water-cooling of plasma facing components and a complex networking of kilometers of pipework will be installed in the plasma vessel to connect all components to the cooling system. An advanced technology was developed in collaboration with industry for the target elements of the high heat flux (HHF) divertor, the so-called “bi-layer” technology for the bonding of flat tiles made from CFC NB31 onto the CuCrZr cooling structure. The design, R&D and the adopted technological solutions of plasma facing components are presented. At present, except the HHF divertor, most of plasma facing components has been already manufactured.

The in-vessel components of Wendelstein 7-X (W7-X) with a total surface of 265 m 2 comprise the divertor and the wall protection. The high heat flux (HHF) and lower heat flux (LHF) target, the baffle, the end plates closing the divertor chamber, a cryo vacuum pump (CVP) and a control coil form one divertor unit. Steel panels and the graphite heat shield protect the wall, including the ports. The HHF target elements, the steel panels and the control coils are manufactured by industry. The remaining components will be manufactured by the Max-Planck-Institute fur Plasmaphysik (IPP) at its Garching workshops. For all components the final acceptance tests will be performed by IPP. This paper summarizes the main aspects for manufacturing, the preceding development and qualification tests as well as the final acceptance tests for the in-vessel components.

The baffles and heat shields of the wall protection of the Wendelstein 7-X stellarator are actively water cooled components based on the same technology. Fine grain graphite tiles are clamped onto a CuCrZr heat sink, which is vacuum brazed to a stainless steel tube. The baffles are part of the divertor and improve the divertor pumping efficiency. The heat shields protect the plasma vessel wall, water piping, cables and the integrated diagnostics. The 170 baffles with 25 variants and 162 heat shield modules with 85 variants comprise a total surface of 33 m2 and 51 m2, respectively. Design guidelines enabled as much as possible the standardization of the fabrication to allow for a more efficient work organization. Individual jigs have been manufactured for each variant in order to weld, bend and mill the different parts of the baffles and heat shields to the required 3D accuracy. At the end of the manufacturing process, each component has been checked and documented according to a detailed quality plan.

320 In-vessel water cooled stainless steel panels, poloidal closure plates and pumping gap panels, covering an area of approximately 100 m2, are used in Wendelstein7-X to protect the plasma vessel. The panels are manufactured at Deggendorf, Germany by MAN Diesel & Turbo SE. The panels consist of a laser welded sandwich of stainless steel plates together with a labyrinth of cooling channels and have a complicated geometry to fit the plasma vessel of Wendelstein 7-X. The hydraulic and mechanical stability requirements whilst maintaining the tight tolerances for the shape of the components are very demanding. The panels are designed to operate at up to an average heat load of 100 kW/m2 and a maximum heat load of 200 kW/m2 with a water velocity of approximately 2 m s−1. High heat flux testing of an un-cooled panel at a time averaged load of 200 kW/m2 for 10 s were successfully performed to support the start up phase of Wendelstein 7-X operation. Extensive testing both during manufacture and after delivery to IPP-Garching demonstrates the suitability of the delivered panels for their purpose.

All in vessel components (IVCs) of W7-X are actively cooled. Inside the plasma vessel about 4 km of pipes will be installed, supplying water to the IVC. 226 cooling circuits with 78 variants are necessary. The cooling circuits enter the cryostat and the plasma vessel through ad hoc flanged penetrations called “plug-ins”, which provide for the vacuum boundary between the plasma chamber and the torus hall atmosphere. The plug-ins are installed inside the W7-X ports. Some of the plug-ins are also used for the diagnostic cables. In total eighty plug-ins will be produced and installed. The inlet/outlet cooling lines are connected to the plug-ins using a welded hydraulic connector. The layout of the cooling lines is rather complex in consideration of the limited space and the routing between many component parts. Additionally the differential thermal expansion of the lines with respect to the supporting structures during the different operation scenarios had to be compensated by ad hoc supports and adjustments in the flexibility of the lines.

The in-vessel components of the WENDELSTEIN 7-X stellarator consist of the divertor components and the wall protection with its internal cooling supply. The main components of the open divertor are the vertical and horizontal target plates which form the pumping gap, the cryo-vacuum pumps and the control coils. The divertor volume is closed by graphite shielded baffle modules and with divertor closures. All these components are designed to be actively water-cooled. For the first commissioning phase planned in 2014, an inertial-cooled test divertor will be installed instead of the actively water-cooled high heat flux divertor. The wall protection consists of graphite-protected heat shields in the higher loaded areas and stainless steel panels in the lower loaded regions. The wall protection cooling circuits are connected through 80 supply-ports via so-called “plug-ins”. It is envisaged to protect the diagnostic ports by panel-type port-liners. Special graphite-shielded port liners are used on the diagnostic injector and the neutral beam injector ports. The in-vessel components are mainly manufactured and tested at the Max-Planck-Institute fur Plasmaphysik in its Garching workshop. Panels, high heat flux target elements and control coils are delivered by industrial partners. Manufacturing of the KiP (“Komponenten im Plasmagefas”) is in plan. Delivery of the components will be in time.