Design and fabrication of divertor base-plate for JT-60U

The divertor plates have been designed and fabricated for JT-60U (JAERI Tokamak-60 upgrade). The bottom part of the vacuum vessel is fully covered with the divertor plates. The divertor plates are subject to a heat load of 20 MW/m² for 5 s in a 30-mm-wide band. The divertor plates consist of 125 base plates with cooling tubes. Each divertor base plate is held on the vessel wall by a fixed support and sliding supports in order to accommodate thermal expansion differences and withstand magnetic forces. The divertor base plates have been designed to take up as little space as possible in order to gain larger plasma volume. High dimensional and positional accuracy was obtained successfully in the divertor base plates fabricated and installed into the JT-60U vacuum vessel. The achieved accuracy of the base-plate height was within 0.6 mm for neighboring base plates