Anatomy of Fusion: The Reactor of the Future

Cadarache, France
Cadarache, a village in Provence in the south of France, is the site of the €12.8 billion pilot nuclear fusion experiment.

Figure 1.

Pilot Fusion Reactor

Views of a pilot nuclear fusion reactor project from a multi-national consortium, ITER. Below is a cutaway of the body of the device including the core where the plasma reaction will take place. On the next spread is a diagram suggesting the reactor's scale.

For years, the concept of obtaining energy from the fusion of light atomic nuclei to form heavier ones has been a siren call of the universe—perhaps the single most compelling potential application of nuclear science. The fuel is essentially unlimited and available worldwide. The radioactive waste is short-lived. Fusion power systems cannot blow up like Chernobyl nor melt down like Fukushima, and the weapons proliferation risk is small—unlike fission.

While some commentators argue that fusion is too far off, the science and technology is actually moving rapidly forward. In the 1970s, fusion scientists were delighted to produce one-tenth of a watt of heat from fusion for 1/100th of a second. By the 1990s they were producing four million watts for five seconds. That is 20 billion times more energy. Now an international partnership of China, the European Union, India, Japan, Russia, South Korea, and the United States is quietly building in southern France a major fusion experiment, called ITER, or the International Thermonuclear Experimental Reactor, expected to go on line by 2020. It is slated to make hundreds of millions of watts from fusion for up to an hour at a time, primarily held back from generating heat for longer periods by the size of the cooling system.

Fusion is the process that takes place at the core of the sun, where fast-moving hydrogen nuclei collide and fuse together to form helium, releasing energy. A power plant would use the isotopes of hydrogen that fuse most readily—deuterium (one proton and one neutron) and tritium (one proton and two neutrons). Both of these fuel sources can be made from seawater, so they are effectively inexhaustible and available to all nations.

But when will electricity from fusion light our homes? Scientists and engineers are confident commercial amounts of power can be made with fusion, but two key questions will remain even if ITER succeeds. Can it be reliable, and can it be cost-effective? Each of the ITER partners is thinking about these questions and trying to win the race to commercialization. American scientists and engineers have begun to study the idea of a fusion pilot plant, one that generates more electrical power than it consumes, putting net electricity onto the grid—a very exciting step. At the same time, the plant would allow the testing of the components for a full-scale, commercial fusion plant. This is where the rubber will really hit the road.

While ITER will prove the feasibility of fusion on a commercial scale, a pilot plant like this would prove that fusion could also be dependable and economical. The superconducting magnets, operating at four degrees above absolute zero, produce a steady magnetic field pattern that levitates the 100 million degree Celsius gas. This is possible because at this temperature the gas is ionized, meaning its positively charged nuclei are separated from its negatively charged electrons. This soup of charged particles heats up to about six-and-a-half times the temperature in the center of the sun. The particles trace out magnetic fields in tight spirals, allowing their trajectories to be precisely controlled by the magnets and shaped to fit in the chamber. This state of matter is called plasma. Indeed, most of the visible universe—our sun and billions of stars in the sky—is in this plasma state. The beams of energetic atoms or microwaves that heat the fuel to these high temperatures come in through ports on the side of the...