What is fusion energy, and what will it take for it to go mainstream?

The world urgently needs a carbon-free, safe, clean and limitless source of energy to provide cheap electricity. Fusion energy has the potential to meet this need.

Japan has pledged to be carbon-neutral by 2050, China by 2060, and the UK has committed to net zero greenhouse gas emissions by 2050. At the same time, the world’s demand for energy will grow substantially. Increasing electrification generated from carbon-neutral sources will be needed. This will not be met in the long-term without new contributions from fusion energy.

Carbon-intensive energy sources will produce diminishing amounts of the world’s electricity. Renewable energy can potentially meet a significant proportion of demand, but it cannot guarantee baseloads because of vagaries in the weather and it is less suited to high-density cities. Electricity from nuclear fission currently provides around 10% of the world’s demand. It is estimated that fusion could contribute a similar percentage in the future.

Fusion is the process that powers the stars. It occurs when atomic nuclei ‘fuse’ together to form a heavier nucleus. In contrast, the fission reactions that currently produce the world’s nuclear energy work by splitting atoms. Temperatures in excess of 150 million degrees Celsius – 10 times hotter than the centre of the sun – are required for fusion to occur on Earth. Unsurprisingly, achieving and controlling these enormous temperatures is a substantial technological challenge. This usually requires using incredibly powerful magnets to contain a hot plasma, preventing it from touching and melting the sides of vessels. Fusion research reactors have achieved temperatures in excess of 300 million degrees Celsius.

Fusion science indicates that fusion energy will require small amounts of fuel, produce very little nuclear waste, and its reactions can be shut down swiftly. It is hoped that fusion can produce enormous amounts of energy from relatively small machines. These features, coupled with high-density energy output, will make them ideal for powering mega-cities.

The urgency of the climate crisis highlights the need to accelerate and intensify experiments to create new forms of energy, including the design and development of fusion machines.

Experiments create options for the future. They provide focal points for learning and innovation, developing new skills and capabilities. Large-scale experiments can create whole new industries, such as when electrification of cities occurred at the end of the 19th century, or in the development of the internet and world wide web.

Experiments are needed for proof of concepts, to test alternative choices, and to hone technical performance. Usually, the greater the number of experiments, the faster the learning curve. Eventually, a dominant design emerges as leading technologists and designers alight upon the best-performing combination of technologies.

The science of fusion is proven and the technical challenges of implementing practical, controlled, reliable and cost-effective fusion energy are being addressed through many experimental programmes. There are government-funded fusion research centres in 26 countries, including the USA, UK, Germany, China, Korea and Japan. Governments have invested billions of dollars in these experiments and are renewing their efforts to win the race in developing reliable fusion energy machines by committing to high-risk, high impact, ‘moonshot’ development programmes.

Experiments in fusion energy have already resulted in advances in a wide range of supportive technologies, such as new materials, robotics and data analytics. It has provided educational and training opportunities and helped develop engineering and construction capabilities in the private sector.

There are a number of different designs for fusion machines. The most common is the tokamak, designed by Russian scientists in the 1950s, which is typically toroidal (doughnut shaped). The tokamak design has evolved as experiments generate more reliable knowledge about what type of machine might work cost-effectively. The Joint European Torus located at the UK’s Atomic Energy Authority in Culham, Oxfordshire is the world’s most successful machine; it holds the record for producing fusion energy of around two-thirds of the power put in to heat the plasma. Since the 1990s the UK has pioneered developments of spherical tokamaks, which are typically smaller than toroidal machines, aimed at compact, cheaper, more reliable configurations.

The stellerator is a more complicated design, in which the vessel is twisted to ease the balance of the flowing plasma, for example, the Wendelstein 7-X in Germany (see below). Another approach to fusion is ‘inertial confinement’, where fusion fuel is instantaneously squeezed by a huge force. This can be done using lasers. For example, the US National Ignition Facility uses the world’s most powerful laser to compress fusion fuel inside small pellets.

There are currently 58 tokamaks, 12 stellerators and five laser ignition facilities around the world, with 24 other configurations. There are 74 experimental fusion reactors currently operating, with 15 more proposed or planned. Of the fusion reactors in operation or proposed, 79 are owned publicly and 20 privately. Private sector fusion companies have recently attracted around $2 billion dollars of investment.

Fusion experiments are advancing by building on the scale and long-term advantages of government investment, complemented by the speed, agility and market discipline of the private sector. Scientific experiments funded by governments are reducing uncertainties and helping progress towards a dominant design, reducing risks for private sector investors.

International collaboration is important because of the scale and complexity of the technological challenges confronting fusion. Large teams of scientists and engineers are needed to work on large-scale machines in order to run the range and number of experiments needed for proof of concept. One of the world’s largest scientific experiments – the fusion research programme, ITER – is currently being built in Cadarache in France. ITER has seven members: the EU, Japan, South Korea, Russia, the US, China and India, 35 countries in all. This vast international demonstration experiment, which is expected to become operational in 2025, had an initial budget of $10 billion and its eventual cost may be quadrupled. Major components of the ITER tokamak reactor are being manufactured in Italy, Spain, Germany, Japan, South Korea and India. Currently 3,000 people work at ITER, with around 15,000 contributing worldwide.

ITER aims to produce 10 times more energy from fusion than is used to produce it, and it and other fusion experiments will involve major advances in science and engineering. It will involve greater understanding of the basic science of plasmas, materials and materials handling, and the management of heat.

The science of fusion is internationally cooperative, but it has often taken place in challenging political circumstances. These arise from meeting its high costs of development and justifying its timescales; fusion power will not feed electricity grids until after the lifespans of the governments making the investments. ITER shows how nations that face military and trade hostilities are prepared to collaborate in scientific experiments, even though it is complicated and demanding. The incentive to do so lies in the prize of limitless, clean and cheap energy.

Fusion experiments advance scientific and technological knowledge crucial for our future and create new economic and industrial opportunities. We also do well to remember President John Kennedy’s entreaty to confront challenges not because they are easy, but because they are hard. In a fractured world there is virtue in demonstrating the fruits of collaborative science, as underpins fusion, and the opportunity it provides for humankind to pursue its innate curiosity.