TURNING ON THE WORLD’S FIRST FUSION REACTOR

NUCLEAR FUSION HAS BEEN ‘RIGHT around the corner’ for decades. But now, that long-promised future is quickly approaching. With tens of billions of dollars on the line, the International Thermonuclear Experimental Reactor (ITER) is almost ready to turn on, 35 years after world leaders, including Ronald Reagan and Mikhail Gorbachev, proposed an international collaboration. While the experimental tokamak – a plasma reactor where extremely hot, charged plasma

creates the conditions necessary for atoms to fuse and release considerable amounts of energy – is one of a handful of very costly ‘miniature suns’ in development around the world, it’s arguably the bellwether for selfsustaining fusion, given the seven countries that share its high cost and are invested in its success.

All this time, engineers have been designing and fabricating the planned one million components needed for the reactor. In May last year, they finally installed the first permanent piece at the reactor’s Provence, France, campus: a steel base for the outer shell of the reactor, which has taken 10 years to forge and weld. This piece is the foundation for the ‘giant thermos’, or cryostat, that holds the reactor and contains its heat. The cryostat will be made from 54 parts combined into four main sections, and it will weigh more than 3 800 tons.

It’s a big step on the path toward 2025, when ITER says all the core parts of the reactor will be installed, fully integrated, and ready to produce its first plasma. That November – to mark the 40th anniversary of Reagan and Gorbachev’s historic US-Soviet Geneva summit – the reactor will begin a month-long process of heating up to 150 million °C, with a trio of heating elements pulling a combined 50 MW of power, enough for about 10 000 homes. That will bring the plasma to a temperature 10 times greater than the Sun’s in the doughnut-shaped reactor to generate as much as 500 MW of energy for brief bursts.

The Sun’s fusion is powered by colliding hydrogen nuclei (atomic number 1) that fuse and make helium (atomic number 2) while releasing energy. But at the heart of the ITER tokamak is a more efficient duo of deuterium and tritium, two hydrogen isotopes that release even more energy when smashed together.

In December 2025, once ITER is hot enough, the first plasma reaction will last just a few milliseconds to indicate that the fully integrated plant is ready for operation. From there, it will go offline for the installation of final parts before the full-scale fusion ITER plans for the mid-2030s. After the lengthy incubation period and progressively longer test plasmas, ITER seeks to hit a state called ignited plasma. This means the deuterium-tritium reaction becomes self-sustaining – no energy is required for the reactions to continue.

While ITER is designed to be a working power plant, it’s also proof of concept for its components. The biggest concern scientists have will be how well each piece of the reactor contains the plasma and its associated heat. Not only is the plasma constantly moving, but any disruption can cool the reactor in a matter of seconds and lose the plasma state.

Inside the reactor, plasma is kept flowing by superconducting electromagnets made of encircling coils of wire. A central solenoid – basically a coil of wire in a corkscrew shape – is bolstered by smaller numbers of external and correction coils. These are made from the superconductors niobium– tin (Nb3Sn) and niobium–titanium (NbTi). All of the coil assembly is held in a high-vacuum pressure chamber (the cryostat).

The magnets are held at cryogenically cold temperatures of –269°C to help create a temperature buffer. Actively cooled thermal shields reduce the radiation heat load that is transferred by thermal radiation and conduction from warm components (vessel) to the cold components (magnets), and the entire 23 000ton tokamak is cooled by circulating water.

The ITER component-by-component focus reflects a larger goal in the nuclear field to make fusion not just feasible, but modular, too. Instead of reactors tailored for specific sites, this generation of nuclear engineers seeks parts that are easier to manufacture, test, and contain. ITER embodies the modular approach by putting successful individual pieces of technology together into the largest-ever full assembly. With existing information on small tokamaks, ITER scientists feel confident in their goals. But the future isn’t a sure thing – until it happens.

THE REACTOR WILL BEGIN A MONTHLONG PROCESS OF HEATING UP TO 150 MILLION °C, WITH A TRIO OF HEATING ELEMENTS PULLING A COMBINED 50 MW OF POWER, ENOUGH FOR ABOUT

10 000 HOMES.

The ITER’s 1 400ton cryostat base is lowered into the tokamak reactor pit.