Nuclear fusion: when will we have our artificial sun?

The ITER project is in full swing these days. Installation of the cryostat, installation of a gigantic 400-ton superconductive coil… the project remains forward-looking and the first deadlines are now fast approaching. A good opportunity to return to this pharaonic scientific project, undoubtedly one of the most important of our era. Guided tour.

Following some feedback that raised the ambiguity of the transition to nuclear fusion weapons, three sentences were rewritten to clarify the point.

ITER is an experience, a proof of concept, a laboratory that does not intend to become a power plant. And to equip it, more than thirty countries (those of the European Union, China, India, Japan, Korea, Russia and the United States) are getting their hands dirty and pocket by providing funds, equipment and infrastructure. But above all, these are some of the greatest brains of fundamental physics and world engineering who align themselves behind a single common objective: to cook a little Sun, just that!

The stars, including our favorite star, all have the particularity of being huge nuclear power plants, operating continuously. Much of their existence comes down to a series of highly energetic fusion reactions that humans have dreamed of domesticating for ages. But it is not tomorrow that we will manage to exploit this energy on the spot, and while waiting to reach it (why not with a sphere of Dyson), the only solution remains to recreate the process of fusion on a small scale to control it the mechanisms.

The cooking recipe of a baby sun

And even in small format, the technical challenge is immense. To achieve this, ITER is based on a discovery dating from 1950, born in the wild imagination of Russian physicists Igor Tamm and Andreï Sakharov on an original idea of ​​physicist Oleg Lavrentiev. It is to this trio that we owe a device called tokamak, of which the ITER reactor is the most famous representative to date. Technology has taken a giant leap since then, but the principle remains the same.

To start a nuclear fusion, you first need… atoms to be fused. In the case of ITER, it is a mixture of gases: deuterium and tritium (D-T), two isotopes of hydrogen. But bringing the nuclei of these atoms together to make them merge is not easy: in the absence of their electrons, they are all positively charged and repel each other like two magnets. To make them merge, the two objects must collide at a phenomenal speed. And to reach such a speed, there is only one solution: the temperature. Indeed, on this small scale, no object is frozen: they “vibrate” on the spot, and it is by measuring the average intensity of this agitation that we estimate the temperature on our scale.

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