....But while fusion actually happened during that four-second window, the energy it took to get the reaction going was eight times more than the power that came out. And while experiments have also been done in England, Japan, South Korea and a few other countries, no one has yet reached so-called “breakeven,” where a reactor generates net power.
ITER is based on the 'tokamak' concept of magnetic confinement. The fuel, a mixture of deuterium and tritium, two isotopes of hydrogen, is heated to temperatures in excess of 150 million°C. Credit: ITER
The best bet for that milestone lies with a machine calledITER (for International Thermonuclear Experimental Reactor), now under construction in southern France. The 100-foot-tall, 23,000-ton device is a joint project of China, the European Union, India, Japan, South Korea, Russia and the U.S., and will begin generating energy sometime in the late 2020’s.
It will, that is, if all goes well. The truth is that fusion still has some major problems that will have to be solved for ITER, and for any commercial-scale machine that follows. For one thing, the fusion reaction sends neutrons slamming into the reactor walls, making conventional materials such as steel brittle. Engineers have to find something better, and they haven’t done it yet. “Right now,” said Michael Zarnstorff, the Princeton lab’s deputy director for research, “we’re thinking tungsten. But we don’t know yet that it’s good enough.” Another issue is that the superheated gas inside the reactor (it’s known as a plasma, which explains the lab’s name) tends to be unstable. Keeping it under control for more than short time is very difficult.
