What is bootstrap current in a tokamak plasma?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

3D illustration of the interior reaction chamber of a tokamak fusion reactor, showing a large, cylindrical, metallic structure with curved walls and bright light panels. — fusion reactor A tokamak is a device used in nuclear-fusion research for magnetic confinement of plasma.

In a tokamak fusion reactor, the bootstrap current is a toroidal current that is generated spontaneously within the plasma due to a pressure differential, where the pressure is higher in the core than at the edge.1

This phenomenon can be viewed as a type of thermoelectric effect originating from the complex particle dynamics inherent in a toroidal plasma. Because external methods for driving plasma current—such as radio-frequency current drive or neutral-beam injection—often suffer from low efficiency, the bootstrap current is highly significant in nuclear engineering. By reducing the reliance on these external power-intensive systems, the bootstrap current helps facilitate the development of steady-state tokamak reactor designs.1