EUROPE AND JAPAN HAVE BEEN working to assemble a tokamak, smaller than the International Thermonuclear Experimental Reactor (ITER) in southern France, that will be used to study modes of future plasma operation.

The project is part of a joint programme between the Japanese National Centralised Tokamak Facility Programme and the Satellite Tokamak Programme conducted by Europe and Japan as part of the Broader Approach agreement. This agreement, between the European Atomic Energy Community (Euratom) and Japan, aims to support ITER and speed up the use of fusion energy, through research and development for future fusion power plants. Both parties contribute equal financing to the partnership, which started in June 2007 for ten years and an additional three years. A five-year extension was signed in March 2020, launching a second phase of activities.

The Broader Approach agreement covers three main projects: a materials testing facility; the International Fusion Energy Research Centre for advanced plasma experimentation and simulation; and an upgrade of the JT-60 tokamak.

JT-60SA was developed using much of the existing site infrastructure from the Japan Torus-60 upgrade experiment (JT-60U), which cuts project assembly time and costs, but most of the main components have been re-designed and manufactured. QST and Fusion for Energy (F4E) are the implementing agencies responsible for the manufacturing of components, assembly and commissioning of JT-60SA.

SA stands for ‘super, advanced’ because the experiment will have superconducting coils to study advanced modes of plasma operation. Assembly of the JT-60SA device was completed at the National Institutes for Quantum and Radiological Science and Technology (QST) in Naka, Japan in March 2020.

Europe contributed the toroidal field coils, high temperature superconductor current leads, cryostat, cryoplant and part of the power supplies, according to F4E. Japan supplied the poloidal field coils, vacuum vessel and in-vessel components, basic power supplies, thermal shields, cryostat port extensions, assembly, disassembly and basic remote handling tools.

The first JT-60SA component — the 250t, 13m diameter cryostat base — was installed on site in January 2013. The base was manufactured by IDESA in Aviles, Spain, with final machining and pre-assembly carried out by Asturfeito under the supervision of Ciemat.

In 2015, the first EU power supplies were delivered and installed, followed by the superconducting magnet power supplies and switching network units.

Installation of the cryoplant took around 12 months and was completed in December 2016. The 18 toroidal field coils — the most complex EU contribution — were tested at nominal temperature and current in the Saclay facility in France, before being delivered to Naka over a couple of years. Assembly of the toroidal field magnets was completed in May 2018. Then the poloidal field coils were installed in their final positions, the thermal shield was erected, the central solenoid inserted, and the cryostat erected and sealed around the machine. The last step was installing the 45t, 11.5m-diameter cryostat top lid on 30 March 2020, completing seven years of work on the project.

What’s next?

Integrated commissioning will now start, checking in sequence the operation of each system. These include evacuating the JT-60SA plasma chamber and cooling the superconducting coils in the lead-up to first plasma operation in autumn 2020.

The JT-60SA tokamak will be a test-bed for ITER, which is currently around 70% complete, as the two devices have similar plasma parameters, superconducting magnet and cryoplant design, and heating and current drive systems. “The European Union has invested several hundred million euros in the construction of JT-60SA,” said Professor Hartmut Zohm from the Max Planck Institute for Plasma Physics in Garching, Germany. “Together with other tokamaks — such as ASDEX Upgrade at Garching — JT-60SA will help to prepare first for ITER operation and then for a demonstration power plant.”

Europe is contributing almost half of the costs of ITER’s construction, with the other six partners (China, India, Japan, South Korea, Russia and the USA) sharing the remaining cost equally. The project achieved some significant milestones in the first half of 2020, with the arrival of the first poloidal field coil (PF6) from Japan, the first three toroidal field coils arriving on site, and positioning of the 1250t cryostat base in the tokamak pit. ITER is targeting first plasma in December 2025. However, during a June meeting the ITER Organization noted that extended shutdowns affecting manufacturing of key components in countries affected by COVID-19 and the slowdown in some assembly activities may have potential consequences for the project schedule.

Although JT-60SA is half the size of ITER, it will use similar superconducting magnets and a liquid helium cooling system.

JT-60SA’s heating systems will inject targeted microwave energy and high-energy particles into the plasma, which should achieve temperatures of around 200 million °C for up to 100 seconds, offering insight as to how to keep the plasma hot and stable as well as how to handle the power exhaust. It will use deuterium plasmas, rather than the deuterium-tritium operation envisaged for ITER.

JT-60SA’s operations will evolve over its lifespan, according to the needs of the fusion community. In its first years, the tokamak’s main function will be to support the assembly, commissioning and preliminary operation of ITER. As the tokamak closest in design to ITER, JT-60SA will perform modelling to help scientists prepare as much as possible for the beginning of ITER operation. The machine will allow the exploration of ITER-relevant high density plasma regimes well above the H-mode power threshold, with up to 41MW of high power electron cyclotron (EC) resonance and positive and negative ion neutral beam heating.

Once ITER is up and running, the focus of JT-60SA’s research is likely to shift towards preparation for the following generation of fusion reactors (like DEMO), focusing on the demonstration and optimisation of steady-state operation of advanced plasma configurations.