In a magnetic field the particles readily spiral along the field lines but diffuse only slowly across them.
JET is the largest Tokamak in the world.
The Tokamak In a Tokamak, plasma is heated in a toroidal vessel and confined away from the vessel walls by magnetic fields. The toroidal field which is produced by coils surrounding the vacuum vessel. Additional coils, not shown in the diagram, around the outside of the vacuum vessel, shape and position the plasma. Schematic diagram of a Tokamak.