Nuclear Reactor Aims for Self-Sustaining Fusion

In a few years, an experimental nuclear fusion reactor near Moscow could be the first to yield a self-sustaining fusion reaction. If the Italian-Russian project is successful, it would be a key milestone for fusion power.

The proposed reactor is based on a design developed by Bruno Coppi, a professor of physics at MIT, and principal investigator on the reactor project with Italy’s National Agency for New Technologies, Energy and the Environment. Three similar reactors based on the same design have already been built at MIT. Italian and Russian physicists plan to meet on May 24 to chart a course for the new reactor, called Ignitor, in the first such meeting since the two countries agreed to join forces on the project in April.

Ignitor is a tokamak reactor, a doughnut-shaped device that uses powerful magnetic fields to produce fusion by squeezing superheated plasma of hydrogen isotopes. As an electric current and high-frequency radio waves pass through the plasma, heating it to extreme temperatures, the surrounding electromagnetic field confines the plasma under high pressure. The combined pressure and heat causes the hydrogen nuclei to fuse together to form helium in a process that releases tremendous amounts of heat. In a fully functional fusion reactor, this heat would be used to power an electricity-generating turbine.

A much larger, far more complex tokamak fusion reactor–the International Thermonuclear Experimental Reactor (ITER)–is planned for construction in Saint-Paul-lez-Durance, France. ITER, which will be completed in 2019 and ready for full-scale testing in 2026, will be closer to a functioning fusion generator but will not produce a self-sustaining fusion reaction. Ignitor will be a sixth the size of ITER and will test the conditions needed to produce a self-sustaining reaction.

“Ignitor will give us a quick look at how burning plasma behaves, and that could inform how we proceed with ITER and other reactors,” says Roscoe White, a distinguished research fellow at the Princeton Plasma Physics Laboratory.

But Ignitor will only test one key aspect of fusion. “It will give us information that is important, but it won’t give us all the information we need and certainly doesn’t replace ITER,” Steven Cowley, director of the Culham Centre for Fusion Energy in Oxfordshire, U.K. “It’s a demonstration that you can create ignition, but it’s not really a pathway to a reactor.”

Unlike ITER, Ignitor doesn’t include many of the components that a real reactor would require. For example one crucial missing part is the “breeder blanket,” which contains lithium and sits inside the reactor’s magnetic coils, providing a continuous supply of tritium–one of two isotopes fused in the reaction. Ignitor’s design is so compact that there is no room for a test blanket inside its coils.

Another limitation of Ignitor is the fact that its high electromagnetic field causes a significant reduction in the conductivity of most superconducting materials. To get around this, Ignitor relies primarily on conventional copper coils to create its magnetic field. But these coils can only operate for short bursts before they overheat. As a result, Ignitor can only sustain ignition for bursts of four seconds. ITER, which relies on superconducting coils and also draws on a significantly larger volume of plasma, is designed to maintain its peak output for 400 seconds.