1985

International Thermonuclear Experimental Reactor (ITER)

For decades we have heard that fusion power will save the world. All that engineers have to do is find a reasonable, inexpensive, controlled way to fuse hydrogen atoms together to create helium atoms, in the same way the sun does it. This fusion process would create a clean form of energy that could power the world without the risk of nuclear accidents, oil spills, and greenhouse gases.

Engineers have found one way to create hydrogen fusion on Earth: the thermonuclear bomb. The big problem is that it is not controlled. It also requires a conventional nuclear bomb to start the fusion process, which can be messy.

With the International Thermonuclear Experimental Reactor, engineers are trying to work out the construction and operation of a practical fusion reactor. Work began in 1985.

The main cavity of the ITER reactor is shaped like a donut (torus). The basic idea is that a cloud of hydrogen gas will convert to plasma while a powerful magnetic field confines it to a thin, dense ring in the middle of the donut. By running a current through the plasma, it will heat to incredibly high temperatures (100+ million degrees K). If the ring is dense enough and hot enough, the hydrogen nuclei will fuse to form helium atoms. The best kinds of hydrogen atoms to use are deuterium (one proton and one neutron in the nucleus) and tritium (one proton and two neutrons). They produce the most energy, primarily in the form of high-energy neutrons that fly out during the fusion process. Trapping the energy of these flying neutrons and converting it to heat is how the reactor will produce electricity.

Although the principles are straightforward, engineers working on ITER face a host of problems. The giant torus needs to maintain a nearly complete vacuum. The torus walls need to withstand the immense heat. Magnets this powerful are difficult to create and require helium cooling. The flying neutrons may destroy the reactor over time. And so on. It is not clear that ITER will work. For the engineers involved in the project, that uncertainty may add to the fun.

SEE ALSO Trinity Nuclear Bomb (1945), Light Water Reactor (1946), Ivy Mike Hydrogen Bomb (1952), Large Hadron Collider (1998).

The model of the reactor of the International Thermonuclear Experimental Reactor (ITER).