Our Best Shot at Nuclear Fusion Needs Magnets That Weigh as Much as a Boeing 747

Jamie Condiff March 18, 2016

When it’s finally built, ITER will be the world’s biggest experimental tokamak nuclear fusion reactor—and probably our best chance to date for making nuclear fusion work. But engineers are currently toiling with building the damn thing and its magnets are proving to be a challenge.

A toroidal fusion reactor like the the smaller Experimental Advanced Superconducting Tokamak, ITER’s design uses a donut-shaped reactor in which incredibly hot plasma resides. Careful control of intense magnetic fields allows the plasma to be contained in a tight ring running through the center of the donut’s circular cross section—which means that the walls of the structure are never directly exposed to the high temperatures of the plasma. By high, we mean really high: Temperatures of the plasma are expected to reach 150 million degrees. So the magnets better be pretty good.

Indeed, Engineering & Technology reports that the magnets are indeed huge. The one that’s currently being built is 45 feet long, 30 feet wide, and 3 feet deep. They’ll also weigh between 250,000 and 500,000 pounds—which is about the same as a Boeing 747 airplane. The final device will actually use a staggering 18 of the things.

They’re made by winding superconducting cable—125 miles of which has been made especially for the project—around slabs of stainless steel plate, several of which are then stacked together. Pipes are also inserted during assembly, to allow engineers to pump liquid helium through, so that the cables can operate properly during operation.

The whole task involves 26 companies and 600 employees, with construction being carried out in the 3-acre assembly plant pictured above. Phew. Let’s hope it all works!