In-bore laser welding tool for actively cooled divertor cassettes in JT-60SA

In-bore remote pipe welding tool has been upgraded for divertor cassettes of JT-60SA, where all plasma-facing components are actively cooled. Because the cooling pipes are surrounded by divertor cassette frame, pipe welding should be done from the inside of the pipe. The tool was equipped with a mirror to reflect the laser radially. Circumferential welding was performed by rotating the tool while injecting the laser. If fumes and spatters adhere to the laser reflecting mirror during welding, the laser will not reach the groove and the welding will not be stable. Upgrading the welding tool has realized to perform welding tests with a well-protected mirror and stable laser power. A misalignment between pipes at the groove is unavoidable in actual divertor cassettes of JT-60SA. The results of butt welding of short pipes indicated that it was possible not only in the gap but also in the combined state with angular and axial misalignment, covering a larger range than required by the actual cassette. It is notable that welding was possible even with an angular misalignment of 0.9° and an axial misalignment of 0.3 mm, where the maximum gap between pipes was about 0.9 mm.