Analysis and design of the actively cooled JT-60 SA divertor

In the frame of the broader approach activities, Fusion for Energy (F4E) is in charge of the design and manufacturing the JT-60 SA Actively Cooled Divertor (ACD). The ACD will be an upgrade of the already existing Inertially Cooled Divertor (ICD) designed by the Japanese National Institute for Science and Technology (QST). The ACD consists of 36 units in total, each unit being approximately 1.8 m wide and 1.3 m tall. Each unit is composed of a Stainless Steel Cassette Frame that supports the High Heat Flux (HHF) and the Normal Heat Flux (NHF) elements. The HHF components are made of Graphite tiles and a TZM heat sink. They are actively cooled with water at an inlet pressure of 2 MPa. The NHF components are made of Graphite tiles bolted to explosion bonded CuCrZr/SS plates cooled with water at 1.4 MPa. The main difference between the ACD and the ICD is the presence of HHF Elements in the vertical targets, which are then suitable for steady state operation. Due to the additional presence of these elements, the supports have been re-designed in order to sustain the mentioned electromagnetic and thermal loads. The design was aimed also at easing and improving the manufacturing processes, in particular harmonizing all cassette and support variants (e.g. for diagnostics installation) and by making most of the components (cassette frames, NHF supports, etc.) compatible with all ports locations. In this paper, the main design features of the new divertor are described in detail, together with the electromagnetic, thermal and mechanical analyses that have been performed to justify the feasibility of the proposed design. The design justification plays a crucial role in the tendering and manufacturing phases, which has started in June 2022 with the HHF elements and will continue until late 2025 with the manufacturing of the other components and the integration of the divertor units.