Nuclear Fusion - Creating a Star On Earth

What is Nuclear Fusion?

Nuclear fusion is the process by which two light atomic nuclei combine to form a single heavier one while releasing massive amounts of energy.

Fusion reactions take place in a state of matter called plasma — a hot, charged gas made of positive ions and free-moving electrons with unique properties distinct from solids, liquids or gases.

The sun, along with all other stars, is powered by this reaction. To fuse in our sun, nuclei need to collide with each other at extremely high temperatures, around ten million degrees Celsius. The high temperature provides them with enough energy to overcome their mutual electrical repulsion. Once the nuclei come within a very close range of each other, the attractive nuclear force between them will outweigh the electrical repulsion and allow them to fuse. For this to happen, the nuclei must be confined within a small space to increase the chances of collision. In the sun, the extreme pressure produced by its immense gravity creates the conditions for fusion.

Why are scientists studying fusion energy?

Ever since the theory of nuclear fusion was understood in the 1930s, scientists — and increasingly also engineers — have been on a quest to recreate and harness it. That is because if nuclear fusion can be replicated on earth at an industrial scale, it could provide virtually limitless clean, safe, and affordable energy to meet the world’s demand.

Fusion could generate four times more energy per kilogram of fuel than fission (used in nuclear power plants) and nearly four million times more energy than burning oil or coal.

Most of the fusion reactor concepts under development will use a mixture of deuterium and tritium — hydrogen atoms that contain extra neutrons. In theory, with just a few grams of these reactants, it is possible to produce a terajoule of energy, which is approximately the energy one person in a developed country needs over sixty years.

Fusion fuel is plentiful and easily accessible: deuterium can be extracted inexpensively from seawater, and tritium can potentially be produced from the reaction of fusion generated neutrons with naturally abundant lithium. These fuel supplies would last for millions of years. Future fusion reactors are also intrinsically safe and are not expected to produce high activity or long-lived nuclear waste. Furthermore, as the fusion process is difficult to start and maintain, there is no risk of a runaway reaction and meltdown; fusion can only occur under strict operational conditions, outside of which (in the case of an accident or system failure, for example), the plasma will naturally terminate, lose its energy very quickly and extinguish before any sustained damage is done to the reactor.

Importantly, nuclear fusion — just like fission — does not emit carbon dioxide or other greenhouse gases into the atmosphere, so it could be a long-term source of low-carbon electricity from the second half of this century onwards.

Where do we stand on fusion technology development?

Nuclear fusion and plasma physics research are carried out in more than 50 countries, and fusion reactions have been successfully produced in many experiments, albeit without so far generating more energy than what was required to start the reaction process. Experts have come up with different designs and magnet-based machines in which fusion takes place, like stellarators and tokamaks, but also approaches that rely on lasers, linear devices and advanced fuels.

How long it will take for fusion energy to be successfully rolled out will depend on mobilizing resources through global partnerships and collaboration, and on how fast the industry will be able to develop, validate and qualify emerging fusion technologies. Another important issue is to develop in parallel the necessary nuclear infrastructure, such as the requirements, standards, and good practices, relevant to the realisation of this future energy source.

Following 10 years of component design, site preparation, and manufacturing across the world, the assembly of ITER in France, the world’s largest international fusion facility, commenced in 2020. ITER is an international project that aims to demonstrate the scientific and technological feasibility of fusion energy production and prove technology and concepts for future electricity-producing demonstration fusion power plants, called DEMOs. ITER will start conducting its first experiments in the second half of this decade and full-power experiments are planned to commence in 2036.

European Breakthrough

In February 2022 the UK-based JET laboratory smashed its own world record for the amount of energy it can extract by squeezing together two forms of hydrogen.

The experiments produced 59 megajoules of energy over five seconds (11 megawatts of power).

This is more than double what was achieved in similar tests back in 1997.

It's not a massive energy output - only enough to boil about 60 kettles' worth of water. But the significance is that it validates design choices that have been made for an even bigger fusion reactor now being constructed in France.

"The JET experiments put us a step closer to fusion power," said Dr Joe Milnes, the head of operations at the reactor lab. "We've demonstrated that we can create a mini star inside of our machine and hold it there for five seconds and get high performance, which really takes us into a new realm."

The ITER facility in southern France is supported by a consortium of world governments, including from EU member states, the US, China and Russia. It is expected to be the last step in proving nuclear fusion can become a reliable energy provider in the second half of this century.

Operating the power plants of the future based on fusion would produce no greenhouse gases and only very small amounts of short-lived radioactive waste.

Prof Ian Chapman, JET CEO

"These experiments we've just completed had to work. If they hadn't then we'd have real concerns about whether ITER could meet its goals. This was high stakes and the fact that we achieved what we did was down to the brilliance of people and their trust in the scientific endeavour"

The Joint European Torus (JET), sited at Culham in Oxfordshire, has been pioneering this fusion approach for nearly 40 years. And for the past 10 years, it has been configured to replicate the anticipated ITER set-up.

JET can't actually run any longer because its copper electromagnets get too hot. For ITER, internally cooled superconducting magnets will be used.

Fusion reactions in the lab famously consume more energy to initiate than they can output. At Jet, two 500 megawatt flywheels are used to run the experiments.

But there is solid evidence that this deficit can be overcome in the future as the plasmas are scaled up. ITER's toroidal vessel volume will be 10 times that of JET. It's hoped the French lab will get to breakeven. The commercial power plants that come after should then show a net gain that could be fed into electricity grids.

This is a long game and it's significant that of the 300 or so scientists working as JET, a quarter are in the early part of their careers. They will have to carry the baton of research forward.

And here's the problem: the need for carbon-free energy is urgent - and the government has pledged that all electricity in the UK must be zero emissions by 2035. That means nuclear, renewables and energy storage.

There's huge uncertainty about when fusion power will be ready for commercialisation. One estimate suggests maybe 20 years. Then fusion would need to scale up, which would mean a delay of perhaps another few decades.

Many technical challenges remain, however. In Europe, these challenges are being worked on by the Eurofusion consortium, which comprises some 5,000 science and engineering experts from across the EU, Switzerland and Ukraine.

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Information sourced from BBC and IAEA.org