ITER fusion research reactor, computer artwork. ITER, the International Thermonuclear Experimental Reactor, is being designed to test the principles surrounding the generation of power from nuclear fusion, the energy source of stars. ITER comprises a toroidal (doughnut-shaped) chamber in which a plasma (pink) is contained by strong magnetic fields. A plasma is an ionised gas, and its ionisation makes it susceptible to electromagnetic fields. By magnetically compressing and igniting a plasma inside ITER, researchers hope to be able to study the best way of using it to generate electricity. Reactions are due to begin in 2016.