BBC Science Focus

HOW IT WORKS: TOKAMAK ST40

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1 OUTER CASING

This is made from 30mm-thick stainless steel.

2 TOROIDAL FIELD MAGNETS

These confine the plasma and hold it away from the walls. The plasma particles continuous­ly spiral around the tokamak, following the magnetic field.

CENTRAL COLUMN This contains a solenoid (a coil of wire that generates a magnetic field) that keeps a current flowing through the plasma, helping to hold it stable.

POLOIDAL FIELD MAGNETS These control the shape and position of the plasma.

PORTS These let the scientists monitor the tokamak. The ports also allow for injection of fuel (tritium and deuterium).

DIVERTOR REGION Helium produced in the fusion reaction is skimmed from the edge of the plasma at the top and bottom of the tokamak’s inner chamber. Failing to remove this waste would ultimately shut down fusion.

TORUS OF PLASMA This gas of electrical­ly-charged deuterium and tritium atoms will undergo nuclear fusion, with temperatur­es rising to more than 100 million degrees Celsius (seven times hotter than the centre of the Sun). The heat generated in the reaction is extracted from the tokamak, where it can heat water to drive turbines.

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