Science

ITER will soon be equipped with the most powerful magnet in the world

This magnet would be able to lift an aircraft carrier two meters above the ground! Integrated into the heart ofInternational thermonuclear experimental reactor (ITER), it should make it possible to produce an almost unlimited amount of energy, without any carbon emissions. Left this week from the factory of the manufacturer General Atomics, in California, the components of the first module of this magnet are currently in transit to France.

This will undoubtedly be one of the most closely watched convoys: the components must reach the Cadarache nuclear studies center without a hitch, where they will form the central solenoid of the tokamak, the most powerful electromagnet in the world. As a reminder, the ITER project is a nuclear fusion reactor project, supported by a coalition of 35 countries, aimed at demonstrating that it is possible to produce a massive amount of energy without polluting emissions.

Fusion is the source of energy that powers the Sun and the stars: at the heart of these stellar objects, the pressure and temperature are so high that the hydrogen nuclei collide and merge to form helium atoms, releasing a considerable amount of energy in the process. Tokamaks like ITER are designed to reproduce this phenomenon, on a smaller scale; to confine and control the plasma, very strong magnetic fields are needed.

A magnetic field 280,000 times more powerful than that of the Earth

Inside the reactor, deuterium (H2) and tritium (H3) gaseous will be superheated (up to 10 times more than at the heart of the Sun), until they are transformed into plasma. The role of the magnet is therefore to keep this plasma, composed of charged particles, away from any metallic surface, within the vacuum chamber; the extreme temperature inside the machine (over 150 million degrees) would melt any material.

Creating magnetic fields in a tokamak requires several different magnet arrays. Eighteen outer coils, arranged around the ring of the tokamak, produce the toroidal magnetic field, confining the plasma inside the vessel. The six poloidal coils – a set of stacked rings orbiting the tokamak parallel to its circumference – control the position and shape of the plasma. In the center of the tokamak, the central solenoid forms the “spinal column” of the machine; its function is to induce the plasma current and to maintain it throughout the discharge.

It took General Atomics nearly a decade to design this magnet. The last tests were finalized earlier this year and the first solenoid module is now heading aboard a heavy truck to Houston, where it will embark on a ship bound for the south of France. When assembled, the central solenoid will measure 18 meters high by 4.25 meters wide; it consists of six independent coils, each containing 43 kilometers of niobium-tin superconductor. A second module should be shipped in August.

In total, 1,000 tonnes of superconducting systems (cooled to -270 ° C) will generate a magnetic field with a force of 13 Tesla (i.e. a field approximately 280,000 times stronger than the Earth’s magnetic field, which varies from 30 at 60 microteslas); the total magnetic energy will be 51 gigajoules. ” This project ranks among the largest, most complex and demanding magnetic programs ever undertaken Said John Smith, director of engineering and projects at General Atomics.

By the power of this magnetic field, ” central solenoid support structures will have to withstand forces equal to twice the thrust of a space shuttle takeoff », Can we read in a press release. The assembly will not be without difficulties: despite its impressive dimensions, the central solenoid must be positioned to the nearest millimeter!

Objective: to produce 500 MW of power

Hydrogen fusion is an ideal source of energy, both sustainable (deuterium is readily available in water), clean (it emits no greenhouse gases) and safe (the only by-product of the reaction is helium, and tritium, although radioactive, is non-fissile). The risk of a nuclear accident is also unlikely: in the event of a disturbance, the plasma cools in a few seconds and the reactions quite simply stop.

But having a secure and sustainable source of energy remains a dream for the moment. If several tokamaks have already made it possible to initiate fusion reactions, none has ever reached an interesting breakeven point; in other words, none of them managed to produce more energy than they used. The ITER project aims to produce 10 times more energy than it will consume: 500 MW of fusion power for an input power of 50 MW for 400 to 600 seconds. The power output record is currently held by the tokamak Joint European Torus (JET): in 1997, this reactor generated 16 MW of fusion power for a contribution of 24 MW.

Within ITER, the fusion reactions will release very high energy neutrons, which will be ejected towards the walls of the vacuum chamber (where the energy will then be absorbed in the form of heat) or which will react with the lithium in the vacuum chamber. ‘enclosure, thus creating more “fuel” for the reaction – because the tritium needed for the reaction can be produced by the interaction of a neutron and a lithium atom.

The creation of the first plasma is scheduled for December 2025, after which the installation will gradually increase in power, using only hydrogen, in order to test different operating regimes. The use of fuel combining deuterium and tritium is scheduled for 2035. If the project proves successful, it will lay the foundations for the first generation of commercial fusion power plants.

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