Present knowledge about the materials behavior in JT-60

JT-60 first walls were originally composed of a number of tiles made of either molybdenum or Inconel 625 with 20 μm thick TiC coating. These first walls, operated after the bakeout at a temperature of 350°C, provided very clean surfaces as well as superior plasma characteristics during Joule heating discharges. Damage of the TiC-coated first walls was modest and localized to specific spots. However, initial results of the additional heating experiments showed degrading effects of locally melted TiC-coated molybdenum and Inconel 625 on the plasma operation.