Classical diffusion is a key concept in fusion power and other fields where a plasma is confined by a magnetic field. It considers collisions between ions in the plasma that cause the particles to move to different paths and eventually leave the confinement volume. It scales with 1/B2, where B is the magnetic field strength, implies that confinement times can be greatly improved with small increases in field strength. In practice, the rates suggested by classical diffusion have not been found in real-world machines.