How fusion energy works

In a fusion reaction, energy releases when two light atomic nuclei fuse together to form one heavier atom. This is the process that powers the Sun and other stars, where hydrogen nuclei combine to form helium. To achieve fusion, the fuel must heat to extreme temperatures – 15 million degrees Celsius in the centre of the Sun. 

Here on Earth, the most efficient reaction is that between two types of hydrogen – deuterium and tritium. They 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. Containment in a ‘magnetic confinement system‘ keeps the plasma from contamination and cooling by contact with material surfaces.

Magnetic confinement is the approach that UKAEA 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 strong magnetic fields control it.

In a magnetic fusion machine, using deuterium and tritium achieves the maximum fusion power. 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 burning fossil fuels.

A commercial fusion power station will use the energy carried by the neutrons to generate electricity. A blanket of denser material surrounding the machine will slow the neutrons. The heat this provides will be converted into steam to drive turbines and put power on the grid.

---