The tokamak design relies on the confinement of hot plasma with magnetic fields. JET has 32 toroidal magnets and 6 poloidal magnets, which create magnetic fields up to 3.5 tesla – 10 000 times stronger than the Earth’s magnetic field

As the charged plasma particles move around due to their extreme thermal energy they create their own magnetic fields which interact with the fields created by the coils. This complex scenario gives rise to the subject of magnetohydrodynamics – the basis of study into plasma.

JET’s magnets consume the lion’s share of the energy required by the plant – for example the toroidal coils can use up to 380 megawatts. Fortunately superconducting magnets will be used in future tokamaks ( as do some current ones already e.g. Tore Supra, K-star), in place of the copper used in JET. This drastically reduces the energy consumption – although not completely as energy is required to keep superconductors cooled with liquid helium (around -269 degrees Celsius).