Last month, researchers at the National Ignition Facility in California made a significant breakthrough in energy research. For the first time, laboratory-controlled nuclear fusion achieved ignition, producing more energy than was used to start the reaction. Scientists used the world’s largest and most powerful laser array to heat a tiny pellet of fuel, roughly the size of a peppercorn. The total amount of energy in the 192 laser beams used was two megajoules, and the resulting output close to three megajoules.
This is a significant breakthrough because fusion power has seemed just out of reach for decades, a technology that has been perpetually 30 years away. When I was born, Back to the Future had just hit Irish cinemas, and in its final scene a DeLorean travels back and forth between 2015 and 1985 courtesy of a fusion-powered flux capacitor. Having arrived in 2015 by more sedate means, I was disgruntled to discover that fusion power seemed no more likely than other aspects of the film series such as hoverboards or time travel. After 30 years, it was still 30 years away.
The enormous potential of nuclear fusion has been known for over a century. In August 1920, astrophysicist Arthur Eddington gave a lecture at the British Association for the Advancement of Science, where he speculated that stars produced their vast and seemingly endless energy from fusion.
The most popular previous explanation had come from the physicists Lord Kelvin and Hermann von Helmholtz, who suggested gravitational contraction could provide the necessary energy. However, this meant stars would only burn for millions of years, and evidence from geology and biology suggested that the solar system had already existed for billions.
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Correct theory
As it turned out, Eddington’s theory was correct. In the sun’s core, hydrogen atoms fuse together to form helium during a complex process called the proton-proton chain. At its most simple, this can be thought of as four hydrogen atoms producing one helium atom. However, the mass of the helium is 0.7 per cent lower than of the hydrogen. According to Albert Einstein’s famous equation E=mc2, mass and energy are interchangeable and so this lost mass is released as energy. The amount of energy released is equal to mass multiplied by the square of the speed of light, which is an extremely large number, and so small amounts of mass can generate comparatively large amounts of energy.
Nuclear fusion contrasts with nuclear fission, which is how nuclear power is currently generated. In fission, atoms of heavy elements such as uranium are split to form lighter elements, which releases energy. Although the amount of energy generated is considerable, it comes with side effects.
The process creates harmful radioactive byproducts which must be carefully managed, and if the reaction is not properly controlled it can cause a meltdown as at Chernobyl and Fukushima. Although radioactive materials are part of the fusion process, it does not produce long-lived nuclear waste, nor does it generate greenhouse gases.
Meltdown avoided
And because the conditions for fusion require tremendous amounts of energy there is no danger of a meltdown – the reaction simply stops. This, ultimately, is why workable fusion power has proved so elusive. Fusion has been a convenient means of generating clean, limitless energy in entertainment from Iron Man to SimCity. But replicating the energy conditions of the sun is no small feat in the real world.
Attempts to produce those conditions have required vast amounts of energy to generate plasma or laser energy, far more than the reaction outputs. The ITER fusion reactor being constructed in southern France has already cost an estimated €20 billion before it has been completed, much less generated any energy. The National Ignition Facility has had some success, but their experiment only measures the laser energy of the beam, and not the energy required to produce it.
The huge laser array would just about fit into Croke Park, and the three megajoules it produced would run a vacuum cleaner for about an hour. Nevertheless, it is a significant step forward, an important proof of concept. A workable fusion power plant could be within reach. Perhaps in 30 years or so. I’ll not hold my breath for the hoverboard.
Stuart Mathieson is a postdoctoral fellow in the school of history and geography at Dublin City University
