Its advantages are numerous: it generates no CO2, less radioactive waste, and presents no risk of nuclear accidents.

The point on its operation, the projects in progress and when they could succeed.

star energy

Nuclear fusion differs from fission, a technique currently used in nuclear power plants, which consists of breaking the bonds of heavy atomic nuclei.

Fusion is the reverse process: two light atomic nuclei (hydrogen) are fused together to create a heavy one (helium), which releases energy.

It is this process that is at work in the stars, including our Sun.

"Controlling the energy source of stars is the greatest technological challenge ever undertaken by mankind," wrote physicist Arthur Turrell, author of the book "The Star Builders," on Twitter.

Two distinct methods

Fusion is only possible by heating material to extremely high temperatures (on the order of over 100 million degrees).

"So we have to find ways to isolate this extremely hot material from anything that could cool it. This is the problem of confinement", explained to AFP Erik Lefebvre, project manager at the Energy Commission. atomic (CEA).

The first method is magnetic confinement fusion.

In a huge reactor, light hydrogen atoms (deuterium and tritium) are heated.

Matter is then in the state of plasma, a very low density gas.

It is controlled using a magnetic field, obtained using magnets.

This is the method that will be used for the international ITER project, currently under construction in France, and that used by JET (Joint European Torus) near Oxford.

A second method is inertial confinement.

There, very high energy lasers are sent inside a cylinder the size of a thimble, containing the hydrogen.

This is the technique used by the French Laser Megajoule (LMJ), or the most advanced project in this field, the American National Ignition Facility (NIF).

The purpose of the latter is more to demonstrate the physical principle, when the first method seeks to reproduce a configuration close to a future fusion reactor.

Where we are?

For decades, scientists have sought to ensure that the energy produced by nuclear fusion exceeds that used to cause the reaction.

According to the Financial Times, it is this breakthrough which is to be announced on Tuesday by the American NIF.

Demonstrating that obtaining a "net energy gain" is indeed possible is a major step, which has excited many scientists around the world even before its confirmation.

But "there is still a very long way to go" before "a demonstration on an industrial scale and which is commercially viable", warns Érik Lefebvre.

According to him, such projects will take another 20 or 30 years to complete.

Among the challenges: to increase the efficiency of laser sources, and to reproduce the experiment at much higher rates.

Why so much enthusiasm?

Unlike fission, fusion does not involve any risk of nuclear accident.

"If ever a few lasers are missing that do not fire at the right time, or if ever the confinement of the plasma by the magnetic field (...) is not perfect" the reaction will simply stop, explains Érik Lefebvre .

In addition, nuclear fusion produces less radioactive waste than current power plants.

Above all, it does not generate greenhouse gases.

“It is a source of energy that is completely carbon-free, that generates very little waste, and that is intrinsically extremely safe,” summarizes Mr. Lefebvre.

This makes it "a solution for the future for energy problems on a global scale".

However, due to its still early stage of development, it does not represent an immediate solution to the climate crisis and the need for a rapid transition from fossil fuels.

© 2022 AFP