Fusion foundations: the civil challenges underpinning Iter

Cadarache, in the South of France not far from Marseilles, is the site of Iter, the international experiment to build and operate the world’s largest nuclear fusion reactor, to test whether fusion can be a practical method of energy generation; the site is a sunny plateau amid forested hills, with Alps gleaming blue and white in the distance.

The landscape seems parched; the site has been levelled to expose the bare sandstone bedrock, and the (so far) relatively few buildings on the site stand out starkly against the beige ground.

At first glance, there’s little to see. The main focus of activity is what will be the complex that house the fusion machine itself. Iter — originally an acronym for International Thermonuclear Experimental Reactor — is a tokomak, a device which triggers fusion in a plasma, a gaseous mixture of charged subatomic particles made from a mixture of two different types of hydrogen, by confining the plasma within a toroidal vessel and squeezing it with powerful magnetic fields while heating it up. It will be the world’s largest tokomak with an internal  radius of 6m, in total some 19m across and 11m high, enclosing a volume of 1400m3; the electromagnets that will confine the plasma and force it to spin inside the torus will be superconducting, cooled by liquid helium to a few degrees above absolute zero to eliminate the need to supply them constantly with electric current.