The tokamak uses powerful external magnetic fields to confine and control the hot plasma of fusion fuels in a ring-shaped container called a ‘torus’.
It was first developed in the Soviet Union in the 1960s and was soon adopted by researchers around the world due to its enhanced performance compared with other approaches.
The Joint European Torus (JET – pictured), located at Culham Centre for Fusion Energy, is the largest and most powerful tokamak experiment currently operating. MAST Upgrade, also located at Culham, is a more compact and efficient type of device known as a ‘spherical tokamak’.
What’s in a tokamak?
A tokamak is a very complex device – but there are some key components (shown in this interactive diagram) that are crucial for its operation.
Vacuum vessel
The plasma is contained in a ring-shaped vessel under vacuum. This is important to minimise plasma contamination from the gases in air.
Magnetic fields
The hot plasma is contained by a magnetic field which keeps it away from the machine walls. Two sets of magnetic coils – toroidal and poloidal – create a complex 3D field which acts as a magnetic ‘cage' to hold and shape the plasma.
The plasma
The plasma is created by puffing a small amount of the fusion gases (deuterium and tritium) into the vessel and using a high voltage to ‘break down’ the neutral gas to form an electrically charged plasma, which can be controlled by the magnetic field.
Plasma current
A large plasma current is induced in the plasma by a central magnetic coil acting as the primary of a transformer; the plasma is the secondary winding. This current starts heating the plasma up towards fusion temperatures.
Plasma heating
Additional plasma heating is provided by neutral beam injection (where neutral hydrogen atoms are injected at high speed into the plasma) and microwave systems (which heat plasma ions like a microwave oven).
