AbstractIn the reactor design, many components are installed in a narrow space between the superconducting coil and the plasma. In the large helical device (LHD) configuration, the plasma axis is shifted inwards relative to the centre of the two pairing helical coils, and so the space available for thermal insulation, the vacuum vessel, cooling pipes and the first wall is very narrow. The LHD plasma vacuum vessel maintains good vacuum conditions, removes heat from the plasma, and protects superconducting coils from the plasma heat. The vessel is designed to have enough rigidness for stress deformation. In the construction, to facilitate assembly with the helical coils which were completed earlier, the vacuum vessel was fabricated in sections of many small segments. Design and construction of the LHD plasma vacuum vessel is described. These technologies are also quite important to reactor design.