The JT-60SA project succeeded in commissioning test toward the first plasma in 2023 under a framework: the Satellite Tokamak Programme of the Broader Approach Agreement between EU and Japan (H. Shirai et al., 2016). JT-60SA is a tokamak type magnetic confinement device with a superconducting magnet system (Y. Koide et al., 2015) developed and operated at the Quantum Science and Technology institute (QST) in Japan. The magnet system consists of 18 Toroidal Field coils, 6 Equilibrium Field coils, and 4 modules of Central Solenoids, and all the coils are superconducting magnets. In the first commissioning, during 2020 - 2021, JT-60SA has experienced a discharge incident at the EF1 magnet (H. Shirai et al., 2024). As a conclusion of the investigation of the incident, it turned out that the insulation resistance of the magnet system was insufficient. Although the insulation was partly reinforced, the voltage holding under accidentally arising Paschen conditions was not improved enough for the recent operation (OP-1, 2023) (K. Hamada et al., 2024). To prevent the magnet system from discharging during vacuum degradation, a vacuum monitoring system must be prepared to detect vacuum degradation and ramp down the magnet current immediately in case of unexpected vacuum degradation. In this article, the development of the vacuum monitoring system, operational results, and the future plan of the system will be described.

Superconducting (SC) tokamak JT-60SA plays an essential role in fusion research and development by supporting and complementing the ITER project, providing directions to the DEMO design activity and fostering next generation scientists and engineers. Since the short circuit incident at the terminal joints of equilibrium field coil #1 during the integrated commissioning (IC) in March 2021, both EU and JA implementing agencies (IAs) have examined how to ensure safe operation of JT-60SA by mitigating the risk of possible discharge occurrence inside the cryostat. Based on the experience of the global Paschen tests, the IAs have established a strategy of risk mitigation measures, which is a combination of (i) reinforcement of insulation, (ii) avoiding unnecessary voltage application to the coil systems and (iii) immediate de-energization of the coils when deteriorated vacuum conditions are detected. Thanks to the considerable efforts of the Integrated Project Team members, the IC restarted in May 2023. After confirmation of the SC state of the coil systems (TF, EF and CS), the coil energization test and the plasma operation phase 1 (OP-1) started. The first plasma was successfully achieved on 23 October 2023 with a limited value of voltage and current applied to the coils. The plasma configuration control was also confirmed with low plasma current and low auxiliary heating power conditions. Based on the IO-F4E-QST collaboration, activities of JT-60SA have been shared with the IO and provided an important lesson for ITER assembly and commissioning, and will provide an outstanding contribution to fusion research at large. After OP-1, maintenance & enhancement phase 1 (M/E-1) starts from January 2024, in which in-vessel components are installed, and heating and diagnostic systems are extensively upgraded to allow a high power heating experiment planned in OP-2. In order to make the best use of JT-60SA, a newly organized JT-60SA experiment team will refine the research plan for the future high heating power operation phase.

The JT-60 Super Advanced (JT-60SA) tokamak was constructed with very tight tolerances for assembly and handling of heavy components in an enclosed space. Millimetre-order precision was required for the tokamak assembly, not only to avoid mechanical interference, but also to obtain good plasma performance by keeping the magnetic error field low. This effort entailed the development of numerous unique procedures. This paper reports on these procedures, focusing on assembly and testing of the final sector of the vacuum vessel, the central solenoid, top parts of the tokamak, and the in-vessel components.

The construction of a magnet system for the tokamak device of JT-60 super-advanced (JT-60SA) was completed in March 2020. The manufacturing of central solenoid (CS) had been finished in March 2019. The circularity of 4.0 mm is a requirement for CS manufacturing from the point of view of plasma control. The high accurate manufacturing method and jigs had been developed, and the circularity of CS achieves 1.44 mm, which meets the requirement of 4.0 mm. The clearance between the CS and the TF coils is very small, only 14 mm in design. In case the CS touches the TF coils and is subjected to load during operation, the CS can be damaged. Thus the surface dimensions of the CS and the TF coils have been measured before the installation of CS to confirm if the clearance is sufficiently large to avoid the CS crashing into the TF coils. The CS was successfully installed to the tokamak center without any damages in December 2019 as the final step of the magnet assembly of JT-60SA. In this paper, the manufacturing results and the installation of the CS are described.

The JT-60SA Vacuum Vessel (VV) was manufactured as the 10 sectors split in the factory and these sectors were weld-assembled as the 360-degree torus with the design offset value of the weld shrinkage. The dimensions as the 10 m scale torus were well controlled regardless of the thin wall thickness of 18 mm and a large amount of welding line due to the double wall structure and 72 port penetrations. The final VV 20-degree sector was installed into the 340-degree sector of the tokamak with the TF coil and the VV Thermal Shield, and the VV was weld-jointed as a torus. This paper reports the design concept to reduce the safety factor and welding amount to achieve the dimension specified, and the result of the VV manufacturing.

The thermal shield (TS) of JT-60SA which is a superconducting tokamak, is installed to reduce radiation heat load from a vacuum vessel (VV), a cryostat vessel and ports at ambient temperature to superconducting coils at 4 K. The TS is double walled structure with He cooling pipe at 80 K, and is divided electrically in toroidal direction and poloidal direction to suppress eddy currents flowing through the TS during disruption. The TS is required to be installed in a narrow space which is between the VV, the ports, and the superconducting coils. Manufacturing and assembly accuracy of the TS are required to ensure the sufficient space for the relative displacement caused by thermal displacement and seismic load. Customization of mechanical joints in the divided section of the TS is effective process for keeping the required accuracy. Assembly of 340 degrees sector of the vacuum vessel thermal shield has been completed.

The superconducting tokamak JT-60SA is currently being assembled at the QST laboratories in Naka (Japan). Within the European contribution in the framework of the Broader Approach, Spain has been responsible for providing JT-60SA cryostat. The cryostat is a large vacuum vessel made up of 304 stainless steel which encloses the tokamak providing the vacuum environment to reduce thermal loads on the components at cryogenic temperature. It must withstand the external atmospheric pressure during normal operation and the internal overpressure in case of an accident. Due to functional purposes, the cryostat has been divided in three assemblies: the Cryostat Base (CB), the Cryostat Vessel Body Cylindrical Section (CVBCS) and the Top Lid. For transport and assembly reasons the cryostat is made up of 20 main parts: 7 making up the CB and 13 making up the CVBCS (including the top lid). The joints between them rely on bolted flanges together with light seal welds, non-structural fillet welds performed from inside and/or outside of the cryostat. The single wall is externally reinforced with ribs to support the weight of all the ports and port plugs and also to withstand the vacuum pressure. The material is SS 304 (Co < 0.05 wt%) with a permeability (mu(rel)) below 1.1. The CVBCS made of a single wall is a stainless steel shell with a thickness of 34 mm. The CB was manufactured and assembled in-situ in 2013, while the CVBCS has been manufactured, assembled, measured by a Spanish company (ASTURFEITO S.A) and delivered to Japan in November 2017. The paper summarizes the assembly and final measurement of the CVBCS at the factory.

JT-60SA will be the world's largest superconducting tokamak when it is assembled in 2020 in Naka, Japan (R = 3 m, a = 1.2 m). It is being constructed jointly by institutions in the EU and Japan under the Broader Approach agreement. The assembly of its 400-tonne toroidal field (TF) magnet, designed for an on-axis field of 2.25 T, was completed in July 2018. Consideration of its assembly throughout the design process, with associated consultation and testing, allowed high positional accuracy and hence respect for magnetic field tolerances to be achieved.

Port structure in the JT-60SA is designed to access vacuum vessel inside for vacuum exhausts, plasma heating systems and diagnostics etc. from cryostat outside. The port consists of a rectangular pipe, bellows and additional materials such as electrical insulations and connection parts for onsite assembly. The vacuum space as the thermal insulation for superconducting coils is penetrated by the port as the vacuum interfaces between the vacuum vessel and the cryostat so that port structure is required to be structurally integrated against plasma and baking operations and accidental events. This structure must be installed in narrow space, and electrical insulation is functionally designed to avoid the unexpected large eddy current loop. This paper reports the design of port connection structure for the assembly. Port connection parts "Port Extension" and "adjustable plate" are introduced to absorb vertical of 10 mm, toroidal of 8 mm, and port axial of 10 mm error due to the manufacturing and assembly. The bellows are expected to absorb relative displacement of 39 mm only between the vacuum vessel and the cryostat during the operation. The structure is confirmed to withstand the load conditions because stress is estimated to be lower than allowable level by FEM analysis.

In the operation of JT-60SA tokamak device, such loads as electromagnetic (horizontal and vertical loads of 2.5 MN and 7.5 MN, respectively) and seismic are imposed on the VV, and thermal expansion takes place during the baking of Vacuum Vessel (VV). The nine Vacuum Vessel Gravity Supports (GSs) have to support the loads and total dead weight of 400 tons including in-vessel components and compensate thermal deformation. Assembling to realize precise positioning of each GS to the VV is indispensable in the limited space between toroidal field coils. To meet the design requirements described above, a GS is equipped with an assembly of flexible plates (FPs) in its lower part and a stem in its upper part with external thread that is screwed upward on the internal thread of VV stub for installation. Electric discharge machining is applied to form FPs without welding. Narrow gap TIG and electron beam welding are also adopted to suppress welding distortion. By the FEM analysis-based design and successful product manufacturing, we have established a design concept and manufacturing technology of GS that has both stiffness and flexibility. The installation mock-up test of GS has also successfully finished.

The JT-60SA superconducting tokamak is being constructed under dual projects, the EU-JA international collaboration framework and Japanese national programme. To suppress magnetic field error to less than 0.01% with respect to the toroidal magnetic field for good confinement of plasma, QST has developed a precise onsite assembly technology of tokamak components such as vacuum vessel (VV) and toroidal magnetic field coils (TFC) with size of over 10-m scale. Prior to an onsite assembly, the assembly process is carefully simulated in a three dimension CAD model, through which the location and number of the reference points for the assembly are evaluated to determine each component position. In the onsite assembly, the tokamak components are positioned by measuring with the laser tracker of a 0.5 mm spatial resolution and assembled by adjusting with shims and splice plates. The onsite assembly of the VV 340 degrees sector has been succeeded in an allowable accuracy of +8/-4 mm with the 10 m diameter by welding sectors, each of which was circumferentially segmented and manufactured by taking into account the deformation due to the welding. The remaining 20 degrees sector will be installed after the TF coils installation. The metrology developed for the onsite assembly of the JT-60SA is expected to be applicable to ITER whose size is the double of JT-60SA.

The JT-60SA cryostat is a large vacuum vessel made up of 304 stainless steel which encloses the tokamak providing the vacuum environment to reduce thermal loads on the components at cryogenic temperature. It must withstand the external atmospheric pressure during normal operation and the internal overpressure in case of an accident. Due to functional purposes, the cryostat has been divided in three large assemblies: the Cryostat Base (CB), the Cryostat Vessel Body Cylindrical Section (CVBCS) and the Top Lid. The CB was manufactured in Spain and assembled in-situ in 2013, while the CVBC is currently under manufacturing also by a Spanish company and it is expected to be delivered in Naka next year 2017. This paper gives an overview of the manufacturing process and present status of the CVBCS. The manufacturing includes the assembly and testing at the manufacturer workshop as well as the packaging of the component. The reference code being used for the manufacturing is ASME 2007 Section VIII Div.2. (C) 2017 Elsevier B.V. All rights reserved.

The cryostat, made of type 304 stainless steel, is required to fulfil the structural integrity and the vacuum tightness at room temperature, and this paper focuses on the fillet welding mechanical properties as a vacuum seal, especially tensile behavior and fatigue strength. Although the lid at the top is a first major part to be removed when the devices inside would be stated in faulted conditions, the closure process is expected to be low cost and simple, and examined with structural clamping and fillet welding as a vacuum seal since the cryostat is not an usual pressure vessel. This standard strength is designed as a 12 mm leg length and reduction of the welding deposition is surveyed with the other comparative specimens of two leg lengths (6 mm, 9 mm). As a result, the region linearly responded to the loading of the 9 mm specimen sufficiently envelops the standard design strength, and then sufficient fatigue strength is confirmed with the linear response limit load as an amplitude until 2000 cycles. Application of the fillet welding to the closure welding is discussed in this paper.

Manufacturing of JT-60SA Vacuum Vessel (VV) is under the onsite sector assembly, where ten W sectors are to be welded together into a torus. The vessel is 6.6 m height and 5 m major radius and a double wall structure with the thickness of 18 mm and locally 30 mm, and total dimensional tolerance is designed to avoid any interference due to operational displacements. In this paper, two issues are focused: the onsite sector assembly concept and sector welding technology. The assembly concept is a contrivance to fulfil high precision as a large torus W and efficient procedure, and obtained with combination of the direct butt joint and splice plate joint. The welding technology is a method to realize the VV, and investigated on acceptable error sizes with the test pieces for the onsite manipulator welding. Correction method of sector edge is also confirmed by the mock-up. Moreover, application to the onsite sector assembly is discussed. The onsite assembly has been started by this concept with its welding technology. (C) 2015 Elsevier B.V. All rights reserved.

Manufacturing of JT-60SA Vacuum Vessel (VV) is under the onsite sector assembly, where ten VV sectors are to be welded into a torus. The vessel is described as 10 m diameter, 6.6 m height and a double wall structure with type 316L stainless steel of 18 mm thickness and locally 30 mm, and total dimensional tolerance is designed to avoid any interference due to operational displacements. This report introduces two issues such as sector manufacturing and onsite assembly. The sector manufacturing is accomplished in high precision, and the assembly concept is obtained with combination of the direct butt joint and splice plate joint. Moreover, status of the onsite sector assembly are presented.

The assembly scenarios and assembly tools of the major tokamak components for JT-60SA are studied in the following. (1) The assembly frame (with a dedicated 30-tonne crane), which is located around the JT-60SA tokamak, is adopted for effective assembly works in the torus hall and the temporary support of the components during assembly. (2) Metrology for precise positioning of the components is also studied by defining the metrology points on the components. (3) The sector segmentation for weld joints and positioning of the vacuum vessel (VV), the assembly scenario and tools for VV thermal shield (TS), the connection of the outer intercoil structure (OIS) and the installation of the final toroidal field coil (TFC) are studied, as typical examples of the assembly scenarios and tools for JT-60SA.

The JT-60SA cryostat is a stainless steel vacuum vessel (14 m diameter, 16 m height) which encloses the Tokamak providing the vacuum environment (10(-3) Pa) necessary to limit the transmission of thermal loads to the components at cryogenic temperature. It must withstand both external atmospheric pressure during normal operation and internal overpressure in case of an accident.The paper summarizes the structural analyses performed in order to validate the JT-60SA cryostat vessel body design. It comprises several analyses: a buckling analysis to demonstrate stability under the external pressure; an elastic and an elastic-plastic stress analysis according to ASME VIII rules, to evaluate resistance to plastic collapse including localized stress concentrations; and, finally, a detailed analysis with bolted fasteners in order to evaluate the behavior of the flanges, assuring the integrity of the vacuum sealing welds of the cryostat vessel body. (C) 2013 Elsevier B.V. All rights reserved.

This paper focuses on one of the JT-60SA vacuum vessel manufacturing R&D, onsite welding technology of the port joint. The work space is limited inside the vessel, and manipulator application is examined through the simulation and the mock-up trial. As a result, the most difficult port of the upper vertical is successfully weld-jointed. The quality as the product joint and the controllability of the manipulator are assured and perspectives to the other ordinary port joints are discussed with issues gained from this R&D.