Conceptual design of the next generation of W7-X divertor W-target elements

The stellarator Wendelstein 7-X (W7-X) will start operation with an actively water cooled divertor made of target elements armored with CFC (Carbon Fiber Reinforced Carbon) NB31 tiles in 2022. The next step (> 2030) is the installation of a metallic water cooled divertor. Research activities have been launched supported by EUROfusion to develop the next generation of metallic target element. The purpose of the conceptual design is to prepare the first prototyping phase. Stationary loading and water cooling conditions are: 10 MW/m², T_in=30°C, P_static=1 MPa, V_axial=9m/s. Similar to the current divertor, the heat sink is made of CuCrZr. Two kinds of armor materials are considered: pure tungsten and W3.5Ni1.5Cu heavy alloy. One of the main constraints is to keep a weight similar to the CFC design to limit the divertor module weight for assembly. The first analyzed model is a straightforward adaptation of the simplest geometry of a CFC element. Thermal calculations show that the maximal temperatures remain within acceptable limits and 3.5 mm armor layer should be considered as the upper thickness limit. By reducing the distance between coolant and loaded surface the need for swirl flow should be assessed in more details. In addition to modelling, first trials for the industrial manufacturing of the CuCrZr heat sink, armor, bonding procedure have been launched.