The JT-60SA cryostat vessel body has been successfully manufactured and pre-assembled in the Asturfeito S.A. factory located in Aviles, Spain. As a voluntary contributor to the Broader Approach agreement, Spain, through the national fusion research centre CIEMAT, has delivered this component in collaboration with F4E.
The JT-60SA machine is a precursor to ITER: the know-how about optimising plasma operation obtained through the JT-60SA project will be used to develop and benefit ITER.
The cryostat vessel body works as a large containment vessel which will enclose all core JT-60SA components. It consists of 4 individual upper sectors (with a height of around 4 metres) and 8 individual lower sectors (with a height of about 7 metres) which have each been separately positioned and precisely adjusted to form a cylindrical shape which measures about 14 metres in diameter. The cryostat vessel body will provide a thermal insulation and vacuum around the magnet components within the machine in order to ensure that they stay at the cryogenic temperature necessary (at 4 Kelvin) for their superconducting functions. Made of 30 mm single-walled stainless steel, the cryostat vessel body can be likened to a thermos in the sense that together with the thermal shields and suprainsulation (multi-layer insulation) inside its shell, it is able to minimise the energy losses by conduction, convection and irradiation.
Manufacturing and testing of each individual sector has been carried out during four years. Pre-assembly of the sectors while still in the factory is necessary to ensure that the re-assembly at the JT-60SA site in Naka, Japan, runs smoothly and that each of the sectors has the required tolerances. Because all vacuum vessel ports, auxiliary devices, cryolines and supply lines need to be fitted precisely in the 83 different flanges and openings of the cryostat vessel body, it is vital to ensure that all pieces of the sectors fit together. By carrying out the pre-assembly at the factory, it is still possible to carry out adjustments to the components if necessary.
Pre-assembly has been performed in three stages: One by one, the eight lower sectors have been positioned, adjusted and bolted to a supporting system reproducing the cryostat basement in Naka. Later, the four upper sectors have been assembled on a temporary supporting system which lastly has been lifted, positioned, adjusted and then joined on the lower sectors. With pre-assembly and metrology now successfully completed, the sectors are currently being dismantled and will undergo final minor refurbishments to eliminate potential superficial damages that may have occurred during the handling and pre-assembly. After final cleaning and packaging, ownership of the JT-60SA cryostat vessel body will be transferred from Spain to F4E and all sectors will be transported to Naka. All components are expected to arrive in Japan between December 2017 and January 2018 – over a year ahead of the required final assembly date in Naka.
Watch a short clip showing the pre-assembly work of the cryostat here.
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