On December 1, Japan inaugurated the JT-60SA which is considered the world’s largest superconducting tokamak. The structure, responsible for producing energy from nuclear fusion, benefits from the support of the European Union (EU) and is seen as a precursor to the international thermonuclear experimental reactor (ITER) currently being built in France. The latter should enter service in a few years.
The principle of nuclear fusion
Nuclear fusion in a tokamak, like the JT-60SA, is a complex process that aims to recreate the conditions found in the hearts of stars, where atoms fuse to release enormous amounts of energy.
To do this, the tokamak, which is a donut-shaped structure, uses a mixture of light gases, usually hydrogen isotopes like deuterium and tritium. These gases are heated to extremely high temperatures to form a plasma. This is a state of matter where electrons are free to move, creating an electric charge.
The hot plasma is then maintained and confined using powerful magnetic fields generated by superconducting coils which prevent the plasma from coming into contact with the walls of the tokamak, which would cause a loss of energy.
Additional heating methods, such as radio frequency waves or neutral particle beams, are used to increase the plasma temperature to extreme levels that reach millions of degrees Celsius. At such temperatures, the nuclei of atoms acquire high kinetic energy.
When the plasma reaches high enough temperatures, the hydrogen nuclei (deuterium and tritium) begin to fuse to form a helium nucleus, releasing a neutron and a considerable amount of energy.
The energy released in the form of neutrons can be used to heat a fluid, usually a mixture of lithium and beryllium, which in turn produces steam to generate electricity through a turbine.
The main challenge in nuclear fusion is to maintain stable conditions and create a net energy gain. In other words, the amount of energy produced by fusion must exceed that necessary to maintain the process. This will be precisely the main objective of the JT-60SA: to demonstrate that its design can generate more energy than it consumes.
As said in the preamble, the advances and lessons learned from JT-60SA could contribute to the overall fusion research effort and directly benefit ITER (International Thermonuclear Experimental Reactor).
As a reminder, this is a major international initiative aimed at building and operating an experimental nuclear fusion reactor. Members include the entire European Union, Switzerland, the United Kingdom, India, Japan, Russia, China and the United States. The ITER construction site is located in Saint-Paul-lès-Durance, in the south of France.
The project, currently in the intensive construction phase, must go through several operating stages. The first is to demonstrate plasma combustion and generate more energy than is consumed. The next phase is to achieve full fusion where the reactor produces a net amount of energy, with the aim of achieving this by 2035.