Development of the Welded Bellows for the KSTAR Vacuum Vessel

The vacuum vessel of the KSTAR (Korea Superconducting Tokamak Advanced Research) tokamak has 72 ports for diagnostics, plasma heating, vacuum pumping, baking, and cooling. The design and fabrication of the bellows at each port need special care in order to compensate relative displacement between the vacuum vessel and the cryostat. S-type welded bellows were designed based on the port shape, the maximum displacement, and the life cycle. Fatigue strength evaluation using Minor's rule was performed. Rectangular-shaped prototype bellows with outer dimension of 1370 mmtimes1610 mm was fabricated and tested. We confirmed that the bellows had sufficient fatigue strength and vacuum reliability. VALQUA fabricated the bellows including one prototype bellows and 72 main bellows. The fabricated bellows were assembled with the vacuum vessel ports. The assembled port devices are going to be welded on the vacuum vessel body in accordance with the KSTAR tokamak assembly scenario