Thirty years away, and always will be. That is a joke frequently told about commercial fusion power. And it has stood the test of time. In 1957 boffins at Britain’s atomic energy authority (UKAEA) thought they had cracked fusion with a machine called Zeta. But the neutrons pouring from this device, which they hoped were leftovers from the merger of the atomic nuclei of deuterium and tritium (two heavy isotopes of hydrogen) to form helium nuclei, turned out to have a different source. Ever since then, like the fruit dangling before Tantalus, fusion has promised far more than it has delivered.

One way or another, though, the joke will soon be outdated. After decades when fusion projects were the preserve of governments, the past few years have seen a proliferation of private efforts. Some half a dozen of these, backed by hundreds of millions of venture dollars (in a couple of cases by more than a billion), are building, or about to build, prototypes that are one generation away from what they hope will be full-scale power stations. The prize for success, they believe, will be a prime place in the brave new world of carbon-free power generation. You can read the details in my report.

The timescales these firms have in mind suggest that their success or failure will be clear by the early 2030s. And the variety of approaches they use equally suggests that this is fusion’s “put-up-or-shut-up” moment. Either it is ten years away, not 30, or it will never happen.

As part of my research for the article I visited Oxfordshire. The unlikely centre of the world’s aspiring fusion industry is a former naval air base, known in the day as HMS Hornbill and now housing the UKAEA’s Culham Centre for Fusion Energy. This is the site of the Joint European Torus (JET), a large intergovernmental fusion reactor.

Ground has just been broken here for the construction of one of the new prototypes, designed by General Fusion, a Canadian firm. Two local outfits plan to follow suit by the end of next year. These are Tokamak Energy, currently just down the road in an industrial estate called Milton Park, and First Light Fusion, now stationed in a similar park a little to the north of Oxford.

The lure for these companies is JET—or, rather, the expertise those operating it have now developed. Tokamak Energy, indeed, was founded by Alan Sykes, who used to work on JET, but who calculated that its doughnut-shaped torus would be more efficient if redesigned to look like a cored apple.

The inspiration for First Light, by contrast, came from the pistol shrimps studied by its founder, Nicholas Hawker, at Oxford University. These stun their prey with high-pressure bubbles created by clicking their claws (let no one ever suggest that zoology is a subject without practical application). General Fusion derives its high pressure from pneumatic pistons.

A converted second-world-war airfield near the banks of the river known at Oxford as the Isis (though others refer to it as the Thames) may seem an unlikely setting for an industrial revolution. But, if it works, and works at a price people can afford, fusion power could hit a sweet spot of green-ness, scalability, reliability and public acceptability that transforms the energy landscape.

Thanks for reading this edition of the Climate Issue. If you have any feedback, you can reach me here: geoff@economist.com