The stars up above draw their energy from nuclear fusion. And here down below, researchers have been working for the last six decades on ways to harness this tremendous power for use on earth. There’s still a long way to go, and many questions remain unanswered. The international ITER project exists to try to provide these answers.

The ITER (International Thermonuclear Experimental Reactor) test plant is located in Cadarache in southern France. Here, new approaches to solving the outstanding problems are being developed in a cooperation that is unique throughout the world: under EU leadership, seven project partners – China, Europe, India, Japan, Russia, South Korea and the USA – have been pooling their expertise since 1985 in the hope of being able to spark this heavenly fire on earth. ITER is intended to create the conditions for making nuclear fusion technology fit for the energy market. The reactor building was completed in November 2019. Experiments are scheduled to be completed by 2035. [1]

Here you can see the different stages of how the plant came to be built.

The project has an ambitious goal: the aim is for ITER to generate ten times more energy than is actually needed in the first place to start, and sustain, nuclear fusion in the reactor. At the collaborative JET (Joint European Torus) plant at Culham, near Oxford in England, European scientists succeeded as early as 1997 in recovering through fusion more than half of the energy consumed. [2] If everything goes according to plan, the maximum output of the test plant could be as high as 500 megawatts.


How is the ITER tokamak, a torus-shaped type of reactor, going to be kept in continuous operation, and how will the solar fire be sparked within it? Inside the reactor, deuterium and tritium – both of them types of hydrogen – are heated to 150 million degrees Celsius. [3] Under these extreme conditions the atomic nuclei begin to fuse, releasing enormous amounts of energy in the process: according to the Max Planck Institute for Plasma Physics, one gram of this ionised gas – also known as plasma – could release 90,000 kilowatt hours of energy if produced in a fusion power plant. This is the equivalent to the combustion heat of eleven tons of coal. [4]

Since the gas would normally cool down immediately at the reactor wall, and this in turn would put a complete stop to the fusion reaction, ITER researchers have been deploying magnetic fields inside the reactor to confine the plasma and to keep it away from the reactor walls. Acting like a cage, magnetic coils enclose the doughnut-shaped plasma chamber in which the nuclear fusion takes place. The reactor, with a diameter of six metres and a volume of 840 cubic metres, is the largest of its kind in the world. [5] In addition, an electrical current is run through the plasma vessel. The current generates an additional magnetic field that helps to confine and control the plasma. In this way, the energised plasma particles can move without touching the reactor walls – and nuclear fusion is enabled.


The reactor itself is surrounded by a cooling chamber with temperatures as low as minus 269 degrees Celsius inside to enable the superconductivity of electricity in the coils: unlike conventional copper coils, superconducting coils – once they’ve been cooled down to low temperatures – don’t consume any energy after being switched on. As a result, the electricity can flow through the coil almost without loss, thus maintaining the magnetic field while using little power. [6]

Safety aspects of nuclear fusion also play an important role with ITER. In the future, a metre-thick layer of concrete will encase the world’s largest fusion reactor to prevent the escape of dangerous neutron radiation, which is produced during nuclear fusion and deposited in the reactor walls (read more on the effects of nuclear radiation here). Unlike standard nuclear power reactors, however, the nuclear waste from nuclear fusion reactors radiates more weakly and for a shorter period of time. Indeed, most of the nuclear radiation is expected to have subsided after a century. [7] Chain reactions, such as those that can occur in nuclear reactors, cannot do so here. It is impossible for a meltdown to occur in a fusion reactor, as none of the energy sources used – plasma, magnetic field or coolant – is capable of destroying the containment shell from the inside. [8] If any sort of incident were to occur, the nuclear reaction would immediately collapse.

To find out what the ITER fusion reactor will look like, click here.


However, it’s currently unclear as to whether the ITER time schedule can actually still be met. After all, there’s still quite a way to go before the test plant will be ready for operation. For instance, researchers are working on ways to permanently control the 100-million-degree-hot plasma, and the heat escaping from it, in order to make the walls of the combustion chamber withstand the stresses and strains in the long term. [9] A solution also remains to be found for the radioactive waste accumulated by the ITER reactor.

If the ITER experiment succeeds, the essential knowledge of how a reactor works will be used to provide the basis for building the DEMOnstration power plant (DEMO),[JF1] which will have all the functions of a power plant – and is meant to serve as a precursor to the building of the first commercial fusion power plant. [10] DEMO will also be much larger than the ITER test plant. The increased volume is supposed to make it easier to maintain the fusion reaction, and thus to generate energy in continuous operation. Experts expect DEMO to start operation in 2050. [11]