After the validation of the last superconducting toroidal field coils, the CEA's contribution to the construction of the Japanese JT-60SA Tokamak, dedicated to the study of nuclear fusion, is nearing completion. Ten of them (out of twenty) were manufactured under the responsibility of the CEA by GE Power in Belfort. These coils of nearly 16 tons each will fly to Naka in mid-February to join their sisters and integrate the structure of the Japanese Tokamak. These essential components for the Japanese fusion device are part of the International Thermonuclear Experimental Reactor (ITER) extended approach project, an international project for a civil nuclear fusion research reactor currently being built at Cadarache (Bouches-du-Rhône).
On 16 January 2018, the tenth and last toroidal field coil for JT-60SA, produced by GE Power (formerly Alstom) in Belfort, and built under the responsibility of the CEA, successfully passed the final acceptance tests. Ten additional coils are manufactured in Italy by ASG Superconductors, under the responsibility of the research organization ENEA (Agenzia nazionale per le nuove tecnologie, l'energia e lo sviluppo economico sostenibile). The JT-60SA reactor will only use eighteen coils, two (Italian) coils being manufactured in addition in order mainly to mitigate the project risks and be able to rapidly replace a coil in the Tokamak in case of major problem.
All twenty European superconducting coils built for the Japanese JT-60SA reactor were tested at the dedicated cryogenic test facility located at the CEA research centre in Saclay (Essonne). These tests, carried out by a team from IRFU, qualified these large superconducting magnetic coils, electromagnets 7.5m high by 4.5m wide and 45cm thick, under their nominal operating temperature (4.5K; -268.5°C) and current (25.7kA) conditions.
All the coils met the required criteria and underwent a quench test* to determine their temperature operating margin which is the basis for the future success of the JT-60SA Tokamak.
The last two coils, after each having been equipped with their external connecting structure, whose assembly requires submillimetre accuracy, have been firmly installed in their transport packaging. The mass of the two packages is around 31 tons (16 for the coil, 5 for the external structure and 10 for the packaging frame). These two coils will fly in mid-February 2018 on board a specially chartered Antonov 124 wide-body aircraft to Naka where they will meet their 16 older sisters in the Japanese Tokamak structure.
For all these coils, it is therefore a technical and human adventure of more than ten years that will end in the next few days. It has involved many steps from the definition of specifications, design, contractualization, definition, qualification and validation of manufacturing processes and the implementation of a demanding quality control before the first manufacturing starts in December 2013.
JT-60SA is scheduled to be commissioned in the summer of 2020. It will then become the largest tokamak in the world in operation until ITER starts. Its exploitation is already eagerly awaited by the international scientific community.
* The risk of quenching corresponds to the incident return of the magnet from the superconducting state to the resistive state. During such an incident, the energy stored in the magnet will be dissipated into an external resistor to minimize the temperature increase in the magnet and any mechanical stresses that may occur.
Imaging of cryogenic tests and the installation of mechanical structure on superconducting magnets for the future Japanese tokamak JT-60SA © F. Rhodes/CEA