Structural evaluation of a compact, semi-closed W-shaped divertor system for JT-60U

A compact, semi-closed W-shaped divertor system has been designed, fabricated and installed in the JT-60U to replace the open divertor system. The new system consists of inclined divertors, a dome and baffles. To meet the structural requirements, a segmented structure with an electrically insulated flexible gas seal was applied. Using FEM codes, the system's structural integrity was confirmed for the plasma disruptions by electromagnetic and structural analyses, which take into account the effect of halo currents. Substantial reduction of induced electromagnetic forces is attained in the divertor system due to the electrical insulation used for the gas seal structure. In addition, because of its segmented structure, the induced electromagnetic forces on each component unit are found to be limited. The maximum stress intensities and their ranges are obtained within allowable values. Thermal stress arising from the temperature difference between the divertor system and the vacuum vessel during the baking operation is also satisfactory. Furthermore, thermal and thermal stress analyses showed that the plasma facing components have sufficient structural integrity. (orig.)