Permanent magnets could help to optimize the geometry of a future fusion reactor.

Researchers have proposed a simplified design for nuclear-fusion reactors, based on powerful permanent magnets.

Fusion reactors are still at the prototype stage. They confine plasma inside a doughnut-shaped magnetic field and heat it to millions of degrees, with the goal of fusing light atomic nuclei into heavier ones and releasing vast amounts of energy.

One promising design, called a stellarator, normally requires sophisticated superconducting coils to make the plasma twist as it moves inside the doughnut.

While helping his son with a science-fair project, Michael Zarnstorff at the Max Planck Princeton Research Center for Plasma Physics in New Jersey realized that neodymium–boron permanent magnets had become powerful enough to help. His team’s conceptual design combines simpler, ring-shaped superconducting coils with pancake-shaped magnets attached outside the plasma’s vacuum vessel. Like refrigerator magnets — which stick on only one side — these would produce their magnetic field mainly inside the vessel.

The superconducting coils would be easier to make and would leave more space around the vacuum vessel for other key components of a future fusion reactor, the scientists say.