The result is a self-confining ellipsoid of hot gases, roiling and fusing within a reaction chamber.

ECONOMIST: How to get an energy rush without doughnuts

But in Dr Rostoker's reactor, the helium nuclei created by the process of light fission would be speedy enough to escape from the ends of the ellipsoid, where the magnetic field is weakest.

ECONOMIST: How to get an energy rush without doughnuts