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Professor Sir Chris Llewellyn Smith FRS, Mr Chris Carpenter, Mrs Heather Clark and Mrs Jennifer Hay.
UKAEA Culham Science Centre.

In a world with increasing demands for more, cleaner energy, alternative options are urgently needed. Using fusion - the process that powers the Sun - to supply our energy has been a scientific dream for 50 years, but now it is close to a technical reality.

Fusion is a safe and environmentally friendly energy option offering the possibility of a sustainable and long-term energy supply. In a fusion power plant energy is generated by fusing together the nuclei of two light atoms (deuterium and tritium - isotopes of hydrogen). The primary fuels used in fusion are deuterium and lithium. Deuterium is readily extracted from water (there are around 30 g of deuterium in every cubic metre of water), and lithium is an abundant light metal that is used to generate tritium inside the power plant. The lithium from one laptop battery together with the deuterium from a bath of water could supply the total electricity needed by one person for 30 years. This is the equivalent of the energy produced by 40 tons of coal.

'Other attractive features are that the process does not generate any greenhouse gases, such as carbon dioxide, or longterm radioactive waste', says UKAEA Culham Director Chris Llewellyn Smith. 'Unlike some alternative energy sources it is suitable for large-scale generation of electricity - producing baseload electricity all day and every day, rain or shine.'

To get fusion to happen, experimental devices called tokamaks are used to heat a gas (or plasma) to temperatures of 150-200 million °C - ten times hotter than the centre of the Sun. The plasma is kept away from the walls of the device and squeezed together by powerful magnetic fields. The UKAEA's Culham Science Centre hosts the world's largest fusion experiment - JET (Joint European Torus), the current world record holder for fusion power at 16 megawatts.

Conventional tokamaks - like JET - have a doughnut-shaped chamber to hold the plasma; another device at Culham - MAST - is a spherical tokamak. MAST's plasma chamber is more like a 'cored apple'. 'Spherical tokamaks are smaller than conventional tokamaks', says Chris. 'And they have some other operational characteristics that could make them attractive as power plants.'

The UK Government has recognised the potential of fusion to supply a large proportion of the future energy mix.