Nuclear Fusion: à “tore” ou à raison ?

Triggering D-T fusion reactions could provide virtually unlimited energy, but maintaining a stable plasma at high temperatures poses numerous challenges. Thanks to the Chinese EAST tokamak, new avenues are emerging. Will we succeed in overcoming this technological hurdle?

Nuclear fusion involves combining two light nuclei, most often deuterium (D) and tritium (T), to form helium while releasing a considerable amount of energy: a few dozen kilograms of fuel suffice where millions of tons of coal would otherwise be required. Deuterium is abundant in water, but tritium is rare and must be produced, via reactions involving lithium, within the reactor itself.

Extreme temperatures must be maintained

To trigger fusion, the fuel must be brought to a plasma state—an ionized gas heated to approximately 150 million °C. At these temperatures, atomic nuclei can overcome their electrostatic repulsion and fuse. The main challenge is not so much reaching this temperature but rather maintaining the plasma for long enough and at a density high enough for the reactions to sustain themselves—a condition formalized by the Lawson criterion.

Magnetic confinement in tokamaks

Tokamaks use magnetic confinement to keep this extremely hot plasma from coming into contact with the walls. But the plasma is unstable: like a heated fluid, it develops turbulence that carries heat outward and limits confinement. The greater the temperature difference between the center and the edge, the stronger this turbulence becomes.

Pushing the limits of plasma

An empirical limit, known as the Greenwald limit, constrains the maximum density of the plasma. Beyond this limit, violent instabilities (disruptions) occur: the plasma deforms, touches the wall, loses its energy, and can damage the structure. Recent experiments, notably on the Chinese EAST tokamak, show, however, that it is possible to exceed this limit by optimizing ignition conditions and the initial purity of the plasma.

Toward Controlled and Sustainable Fusion

The ITER project is based on a key idea: increasing the size of the reactor to improve confinement. Indeed, a larger tokamak reduces the temperature gradient, and thus turbulence. At the same time, new ignition methods—notably using microwaves to pre-ionize the plasma—aim to create more stable plasmas from the outset. Despite the technical challenges (materials, neutrons, tritium production), the central challenge remains achieving sufficient confinement to make fusion energetically viable.

Listen to the full podcast here

PINT OF SCIENCE FESTIVAL – May 18–20, 2026

Nuclear Fusion: An Energy Issue, a Global Challenge

Harnessing the energy of the stars on Earth is a long-held dream of humanity, embodied by the international ITER project in Cadarache for the past three years. But major challenges remain, such as turbulence and the transport of energetic particles. These issues are being studied using experimental equipment and through simulations on the world’s most powerful computers.

Zoumaï – Wednesday, May 20

Find all the useful information here