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A milestone for fusion power

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Proponents of generating clean energy from nuclear fusion, the reaction that powers the Sun, have had to live for decades with the taunt that a commercial fusion plant always seems to lie 30 years in the future. But the chances that the timescale might become considerably shorter rose with the official announcement on Tuesday that, for the first time, the energy output from an experimental reactor had exceeded the input.

The “net energy gain” at the National Ignition Facility (NIF), part of the Lawrence Livermore National Laboratory in California, was a relatively modest 50 per cent, far below what would be needed for a commercial reactor. But it still marks a scientific milestone that should encourage more investment in fusion research and development from both private and public sectors.

This achievement follows an encouraging flow of technical and financial news over the past year or so. In February the Joint European Torus in the UK recorded a world record energy output, though this was less than the power required to fire up the reaction. Funding for the growing band of fusion companies, while still far below the level for counterparts in other energy sectors, has doubled over the past year to reach a total of $5bn.

The challenge will be to balance excitement about a symbolically important moment with realism about the gigantic technical and engineering challenges required to translate its promise into a power station. Some initial reactions to the NIF news have come perilously close to hype, using phrases such as “huge breakthrough” and “holy grail”, which risk subsequent disenchantment.

There is even uncertainty about the best overall approach to a fusion reaction. In the “inertial confinement” process used by NIF, 192 laser beams focus simultaneously on a fuel capsule about the size of a peppercorn that contains two isotopes of hydrogen: deuterium and tritium. The resulting implosion fuses the atoms together into helium while releasing vast amounts of energy.

Although there are other inertial confinement projects — for example First Light, a UK company that fires projectiles at the fuel pellet — most fusion labs favour the alternative “magnetic confinement” approach that holds superheated deuterium-tritium fuel in a doughnut-shaped reactor with powerful magnets. The biggest by far is ITER, a $23bn international experiment under construction in France.

For either approach to lead to a cost-effective power station, almost every aspect of today’s experimental reactors needs transforming. The US Department of Energy designed the $3.5bn NIF to simulate nuclear explosions for weapons testing, so a lot of work will be needed to adapt the procedures for civil power generation. And though NIF has passed the “net energy gain” threshold, meaning output was higher than the direct laser input, it is still much lower than the overall energy required from the grid to operate the experiment.

The tens of billions of dollars spent over several decades in fusion research and development are substantial when viewed in isolation. They are tiny, though, compared not only with other forms of energy — from renewables to fossil fuels — but also with the huge potential rewards from having a new power source that is almost carbon-free in its operations and does not depend on limited raw materials or the vagaries of wind and sunshine.

Ramping up fusion R&D should not distract from the need to improve the proven nuclear fission technology that powers existing power stations, particularly by introducing a new generation of small modular reactors. But the cost-benefit analysis would favour more investment in fusion even if it had just a 50 per cent chance of coming to fruition.

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