Controlled nuclear fusion – a clean, near-perpetual source of energy – would revolutionize the world. In recent years, significant steps on the path to a fully operational, efficient fusion reactor have been made, and this week another milestone has been reached: German engineers from the Max Planck Institute have successfully fired up their nuclear fusion reactor, announcing that they have managed to suspend plasma for the first time.
Their 16-meter-long (52-foot-long) experimental fusion reactor, Wendelstein 7-X (W7X), is one of the largest in the world. It took 19 years and €1 billion ($1.1 billion/£715 million) to complete, and contains over 425 tonnes (470 tons) of superconducting magnets, all of which need to be cooled to absolute zero. Within it, the process that operates at the heart of stars can hypothetically take place.
In order to generate energy, extremely high temperatures are required; the center of our own Sun, for example, has temperatures of up to 15 million degrees Celsius (27 million degrees Fahrenheit). At these temperatures, and with the aid of an effect called “quantum tunneling,” atoms of the lightest elements (hydrogen and helium) become energetically excited. At a high enough “ignition temperature,” they begin to collide and fuse, releasing energy and forming heavier elements.
The first suspended plasma within the W7X reactor. IPP
At this temperature, a cloud of incredibly excited molecules called plasma is formed. One of the key stages of nuclear fusion is to stabilize and contain this plasma, so that continuous nuclear fusion can occur. The plasma must not touch the cold vessel walls of the reactor, and so it has to be contained by extremely powerful magnetic fields.
The engineers announced that they have finally managed to do this with their “stellarator” experimental reactor. Lasting for only one-tenth of a second, the one-milligram sample of helium gas was heated by a 1.8-megawatt laser pulse; it reached a temperature of one million degrees Celsius (1.8 million degrees Fahrenheit).
“We're very satisfied,” said Hans-Stephan Bosch, of the Max Planck Institute for Plasma Physics in Greifswald, in a statement. “Everything went according to plan.”
— MPI für Plasmaphysik (@PlasmaphysikIPP) December 10, 2015
Although a sustained hydrogen plasma is the ultimate objective, the team this time used helium. “This is because it’s easier to achieve the plasma state with helium,” explains project leader Professor Thomas Klinger. “We’re not changing over to the actual investigation object, a hydrogen plasma, until next year.”
This represents one of the many steps required to obtain a fusion reactor. The German stellarator will not actually be used to produce any energy – it merely exists to show that suspending plasma is possible.
Another key feature of a viable nuclear fusion reactor is that it has to produce more energy than it takes to initiate the process. Fortunately, this was achieved last year by the National Ignition Facility (NIF) in the United States, but only just.
A rival fusion reactor design, the “tokamak,” is currently being built in France by a multinational effort of scientists and engineers. The International Thermonuclear Experimental Reactor (ITER) takes the form of a doughnut-shaped containment vessel. Due to a series of technical problems and rising construction costs, however, it has yet to carry out its first experiment, meaning that the German stellarator has pipped them to the post.