Manufacturing and joining technologies for helium cooled divertors

• The manufacturing and joining technologies developed at KIT for helium cooled divertors are reviewed and critically discussed.
• Various technologies have been pursued and further developed aiming divertor components with very high quality and sufficient reliability.
• Very promising routes have been found for which however still R&D works are necessary.
• Technologies developed are also useful for other divertor and even blanket concepts, particularly those with tungsten armor.

In the helium cooled (HC) divertor, developed at KIT for a fusion power plant, tungsten has been selected as armor as well as structural material due to its crucial properties: high melting point, very low sputtering yield, good thermal conductivity, high temperature strength, low thermal expansion and low activation. Thereby the armor tungsten is attached to the structural tungsten by thermally conductive joint. Due to the brittleness of tungsten at low temperatures its use as structural material is limited to the high temperature part of the component and a structural joint to the reduced activation ferritic martensitic steel EUROFER97 is foreseen. Hence, to realize the selected hybrid material concept reliable tungsten–steel and tungsten–tungsten joints have been developed and will be reported in this paper.In addition, the modular design of the HC divertor requires tungsten armor tiles and tungsten structural thimbles to be manufactured in high numbers with very high quality. Due to the high strength and low temperature brittleness of tungsten special manufacturing techniques need to be developed for the production of parts with no cavities inside and/or surface flaws. The main achievement in developing the respective manufacturing technologies will be presented and discussed.To achieve the objectives mentioned above various manufacturing and joining technologies are pursued. Their later applicability depends on the level of development including their transferability to the component. Hence, specifying design and requirements for the components of interest will determine appropriate time and criteria for selecting most promising technologies. Although the considered technologies are mainly developed for the HC divertor it is worth to note that they are also useful for other divertor and even blanket concepts, particularly those with tungsten armor.