Status of a European Standard for the protection of helium cryostats against excessive pressure

The overpressure protection of various types of cryogenic vessels is covered by a number of International Standards. Helium cryostats, however, include additional components such as superconducting magnets and cavities, electrical heaters and control valves with associated piping, which significantly influence the potential risk. At the European Committee for Standardization CEN, a new working group was hence founded as CEN/TC 268/WG6, dealing with ‘Specific helium technology applications’. Its aim is to develop a European Standard for the protection of helium cryostats against excessive pressure that is harmonized with the European Pressure Equipment Directive. It will cover the typical conditions in accidental scenarios in order to harmonize the risk assessment as well as design practices for the pressure relieving systems. We report about the general concept of this new Standard, its structure and content, and the actual status of the project

Completion of JT-60SA construction and contribution to ITER

Construction of the JT-60SA tokamak was completed on schedule in March 2020. Manufacture and assembly of all the main tokamak components satisfied technical requirements, including dimensional accuracy and functional performances. Development of the plasma heating systems and diagnostics have also progressed, including the demonstration of the favourable electron cyclotron range of frequency (ECRF) transmission at multiple frequencies and the achievement of long sustainment of a high-energy intense negative ion beam. Development of all the tokamak operation control systems has been completed, together with an improved plasma equilibrium control scheme suitable for superconducting tokamaks including ITER. For preparation of the tokamak operation, plasma discharge scenarios have been established using this advanced equilibrium controller. Individual commissioning of the cryogenic system and the power supply system confirmed that these systems satisfy design requirements including operational schemes contributing directly to ITER, such as active control of heat load fluctuation of the cryoplant, which is essential for dynamic operation in superconducting tokamaks. The integrated commissioning (IC) is started by vacuum pumping of the vacuum vessel and cryostat, and then moved to cool-down of the tokamak and coil excitation tests. Transition to the super-conducting state was confirmed for all the TF, EF and CS coils. The TF coil current successfully reached 25.7 kA, which is the nominal operating current of the TF coil. For this nominal toroidal field of 2.25 T, ECRF was applied and an ECRF plasma was created. The IC was, however, suspended by an incident of over current of one of the superconducting equilibrium field coil and He leakage caused by insufficient voltage holding capability at a terminal joint of the coil. The unique importance of JT-60SA for H-mode and high-β steady-state plasma research has been confirmed using advanced integrated modellings. These experiences of assembly, IC and plasma operation of JT-60SA contribute to ITER risk mitigation and efficient implementation of ITER operation