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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° 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° 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. [ABSTRACT FROM AUTHOR]

Disassembly of the JT-60U torus was started in 2009 after 18 years of D 2 operations and was completed in October 2012 for assembling the JT-60SA torus at the same position. The JT-60U torus was featured by the complicated and welded structure against the strong electromagnetic force, and by the radioactivation due to deuterium–deuterium (D–D) reactions. Since this work is the first experience of disassembling a large radioactivated fusion device in Japan, careful preparations of disassembly activities, including treatment of the radioactivated materials and safety work, have been made. During the disassembly period over 3 years, careful measures against exposure were taken and stringent control of exposure dose were implemented, and as a result, accumulated collective effective dose of ∼41,000 person-day to workers was only ∼22 mSv in total and no internal exposure was observed. About 13,000 components cut into pieces with measuring the contact dose were removed from the torus hall and stored safely in storage facilities. The total weight of the disassembly components reached up to ∼5400 tonnes. Most of the disassembly components will be treated as non-radioactive ones after the clearance level inspection under the Japanese regulations in the future. The assembly of JT-60SA has started in January 2013 after this disassembly of JT-60U torus. [ABSTRACT FROM AUTHOR]

Abstract: The tokamak machine monitoring and control system has been developed to avoid machine damages in JT-60 safety operation. It monitors the JT-60 mechanical structures and other sub-components to maintain their conditions. The system adopts the CAMAC digitizers, the Signal Transfer Unit (STU), and the hard-wired interlocks. Over 20 year, it has never been affected by any major troubles except a water leakage in toroidal field coil (TFC). The TFC monitoring system has been developed for the TFC safety with the water leakage from a cooling water channel. It has improved the reliability and efficiency of the TFC operation. [Copyright &y& Elsevier]

Abstract: Burn control simulation experiments were conducted in non-burning DD plasmas by using a burning plasma simulation scheme in JT-60U. In the burning plasma simulation scheme, two neutral beam (NB) groups were used, where one simulates α-particle heating and the other simulates external heating. The stored energy and the neutron yield rate were controlled at nearly constant values in both ELMy H-mode plasma and reversed shear (RS) plasma with an Internal Transport Barrier. In these plasmas, the NB power for the external heating simulation increased/decreased when the NB power for the α-particle heating simulation decreased/increased. Variation of the NB power for the external heating simulation was larger in the RS plasma than that in the ELMy H-mode plasma, indicating that larger control margin is necessary for the RS plasmas. In order to understand the detailed physical mechanism for the difference between ELMy H-mode and RS plasmas, we conducted numerical analysis using a 1.5-dimensional transport code. This calculation indicates the larger variation experimentally observed in the RS plasma could not be explained by the difference of the thermal diffusivity profiles or its temperature dependence. [Copyright &y& Elsevier]