Biggest Fusion Reactor Has Found Its Heart

The International Thermonuclear Experimental Reactor (ITER) is more than just an exercise in extreme engineering. It is a decades-long effort involving 35 countries, and the stats of the machine highlight the cooperation and expertise of that talent pool.

When completer, ITER will be able to withstand temperatures 10 times hotter than the core of the Sun (150 million degrees Celsius) while also keeping certain components of itself near absolute zero (-273.15 degrees Celsius).

At the heart of this engineering miracle is a 3,000-ton magnet system central to creating an "invisible shield" that keeps superheated plasma contained long enough to kickstart a fusion reaction.

Last 30 April, the ITER team announced that the last piece of this magnetic puzzle—the Central Solenoid—has been built and tested in the U.S. and is now ready for assembly at the ITER facility in France.

Once assembled, this solenoid will be the world’s most powerful magnet. The magnet is so powerful, in fact, that it’s capable of completely levitating an aircraft carrier, according to an ITER press release. It will be contained inside an "exoskeleton" — made of 9,000 individual parts from eight U.S. suppliers—which will support the Central Solenoid as it generates extreme forces capable of kickstarting a fusion reaction.

Although ITER is fundamentally different from our Sun (of course), it does work in a somewhat similar fashion. The Sun uses a "too big to fail" fusion regime—its transparent mass (330,000 times more than that of the Earth) is enough to fuse hydrogen nuclei into helium. On Earth, however, scientists need to compensate for this lack of mass with even more heat.

At a certain temperature threshold, deuterium, and tritium—isotopes of hydrogen that will be used as fuel in ITER—overcome electromagnetic repulsion via quantum tunneling and fuse. Some quick calculations using everyone’s favorite equation e=mc2 show that converting a little mass can give you tons of energy.

ITER’s 10,000 tons worth of superconducting magnets (with a combined energy of 51 gigajoules) will maintain the plasma for long enough at high enough temperatures for this fusion reaction to take place. By the scientists’ estimates, ITER should produce 500 megawatts of power for only 50 megawatts of input heating power—a 10 fold increase.

However, that’s still a long ways off, as recent ITER estimates place the reactor’s first plasma date at around 2035. But once this gargantuan machine of human ingenuity is completely, we will have truly bottled a star—or, at least, a close approximation of it.