In a fusion reaction, energy is released when two light atomic nuclei are fused together to form one heavier atom. This is the process that powers the Sun and other stars, where hydrogen nuclei are combined to form helium.
To achieve fusion, the fuel must be heated to extreme temperatures – 15 million degrees C in the centre of the Sun. Here on Earth, the most efficient reaction is that between two types of hydrogen – deuterium and tritium – which only fuse at temperatures over 100 million degrees Celsius. At these temperatures the fuel becomes an electrically charged gas or plasma.
This incredibly hot plasma is extremely thin and fragile, a million times less dense than air. To keep the plasma from being contaminated and cooled by contact with material surfaces it is contained in a magnetic confinement system.
Magnetic confinement is the approach that Culham and many other laboratories are researching to provide energy from fusion. The fusion plasma is heated and confined in a ring-shaped bottle known as a tokamak, where it is controlled with strong magnetic fields.
In a magnetic fusion device, the maximum fusion power is achieved using deuterium and tritium. These fuse to produce helium and high-speed neutrons, releasing lots of energy per reaction. This is approximately 10,000,000 times more energy per kg of fuel than is released in burning fossil fuels. A commercial fusion power station will use the energy carried by the neutrons to generate electricity. The neutrons will be slowed down by a blanket of denser material surrounding the machine, and the heat this provides will be converted into steam to drive turbines and put power on to the grid.
