The tokamak

We are researching the tokamak – the most successful fusion concept yet developed.

Overview

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’.

The Soviet Union first developed the tokamak in the 1960s. Researchers around the world soon adopted it due to its enhanced performance compared with other approaches.

The Mast Upgrade tokamak

MAST Upgrade is a compact and efficient type of device known as a ‘spherical tokamak’.

The MAST Upgrade tokamak.
A tokamak is a very complex device – but there are some key components that are crucial for its operation.

How the tokamak works

MAST Upgrade tokamak vacuum vessel.
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.
MAST Upgrade tokamak magnetic fields.
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.
MAST Upgrade tokamak 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.
MAST Upgrade tokamak plasma current.
Plasma current – a large current is induced in the plasma by a central magnetic coil. This current starts heating the plasma up towards fusion temperatures.
MAST Upgrade tokamak plasma heating.
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).
MAST Upgrade tokamak plasma exhaust.
Plasma exhaust – excess heat from the hot fusion plasma is exhausted using a magnetic divertor; streams of plasma are diverted into special heat resistant plates at the top and bottom of the tokamak.