The extraordinary, but elusive, promise of fusion energy
What if there was a way to solve all our energy woes through a single technology? A technology that could provide “virtually limitless energy”? One that emitted zero greenhouse gas emissions and minimal waste and that wasn’t subject to the whims of the weather?
This is the promise teased by “nuclear fusion energy”, a promise it has floated for decades, but never delivered upon. Despite nearly a century of research, and billions of dollars in funding, fusion energy remains out of reach for scientists, engineers, and the politicians alike. So, what is so difficult about generating energy through nuclear fusion? And will it ever help solve our numerous energy woes?
What is fusion energy?
The inspiration for fusion energy lies in the centre of the sun. Under the extremely hot, and dense conditions that prevail in the centre of a star such as our own, individual nuclei of hydrogen travel at such high speeds, that they can collide and fuse together to form a helium nucleus, releasing enormous amounts of energy in the process.
The cause of this immense energy release is owed to perhaps the most famous scientific discovery of all time: Einstein’s famous E=mc2, also known as the equivalence of mass and energy. When two hydrogen nuclei fuse together, the helium nucleus that results happens to weigh a little less than the combined weight of two hydrogen nuclei before it. According to Einstein’s equation, the little bit of lost mass is converted into an immense amount of energy, which provides the major energy source for all the stars in the universe.
As soon as the process of nuclear fusion was discovered, its invaluable potential as an energy source was recognised. If the only fuel that is required is hydrogen, the most abundant element in the universe, then fusion power appears to offer us an essentially infinite energy source.
The amount of energy released per kilogram of hydrogen, furthermore, would be close to four million times the amount obtained from burning coal or oil, whilst the reaction would emit zero greenhouse gases and unlike it’s cousin nuclear fission, does not create radioactive waste or carry the risk of nuclear meltdown.
For nearly a century now, scientists have attempted to harness the energy offered by fusion power and unlock its unparalleled potential. And yet despite years of research and billions of dollars of funding, the world remains without a viable nuclear fusion reactor, so what is so especially challenging about designing a nuclear fusion reactor?
Building the Sun on Earth
To harness the energy produced by the fusion of two hydrogen nuclei, you must first bring these nuclei together. Because the two nuclei will carry the same electrical charge, they’ll experience a force, known as the electrostatic, or Coulomb force, that will push them apart. To overcome this force, and be able to fuse together, the two hydrogen nuclei need to be travelling at an immense speed, which requires energy, heaps of energy.
In the sun, this isn’t so much of a problem. The immense gravitational weight and extremely high temperatures encountered within its depths accelerate individual hydrogen nuclei to the speeds necessary to ignite fusion. To replicate a fusion reaction here on Earth, you essentially must find a way to do the same thing, which is no easy feat.
To recreate the environment of the Sun, fusion scientists usually heat up the hydrogen fuel to such an extreme heat that it forms a substance known as ‘plasma’. However, this is where the problems start to begin.
Plasmas not only require immense amounts of energy to be generated, but they are notoriously difficult to handle and their volatility has thwarted many promising attempts to generate fusion energy.
The most expensive fusion reactors are still plagued by issues arise from the precariousness of handling over 100-million-degree plasmas, the physics of which scientists are still trying to understand. Even when reactor designs are able to overcome some of these problems, such as through the ingenious ‘tokamak’ design or through the use of ‘superconductor’ materials, they are still held back by what’s known as ‘energy positivity’ problem. To heat matter up to the plasma state necessary for fusion requires a great deal of energy, much more than can be harnessed from the fusion reaction itself.
So, will fusion power be available anytime soon?
After decades and decades of challenges, and failures, the quest to harness fusion energy still marches steadily on, and benchmarks towards viable fusion energy slowly, but surely, are reached. In February of this year, the UK-based Joint European Torus (JET) reactor set a new world record for amount of energy produced in a single fusion reaction, whilst in April of 2021, the US National Ignition Facility (NIF) was able to recoup 71% of the energy inputted into the reaction, in what was seen as a major step forward.
However, despite these achievements and the continuous work of thousands of scientists, most scientists don’t expect fusion energy to meaningfully contribute to the world’s energy mix until at least the second half of this century. The most elaborate fusion reactor project to date, the International Thermonuclear Experimental Reactor (ITER), is still under construction and is only set to conduct full experiments in 2035.
To address the world’s pressing energy needs, namely the incidence of energy poverty and the urgent need to decarbonise our energy systems, it appears that we’ll need to focus our attention on renewables, battery storage, efficiency measures and behavioural change. Fusion power, for the time being will be nought but a far-off dream, teasing us with its promise, but constantly remaining just out of reach.