Imagine dropping a pea-sized capsule through a spherical chamber and hitting it with a colossal bolt of laser energy as it falls. If the capsule contains a mixture of deuterium and tritium, two heavy versions (isotopes) of hydrogen, then the atoms may fuse, turning into helium and emitting fast neutrons as they do so. Those neutrons and their accompanying radiation can heat molten salts around the walls of the chamber and that heat can be used to power industrial processes – or to boil water and generate electricity through a steam turbine.

That’s the dream of a firm called Xcimer, one of the more ingenious fusion energy startups, based in Colorado. Three years ago, on 5 December 2022, at the Lawrence Livermore National Laboratory in California, this technique was used to reach a significant milestone in the search for near-limitless energy from fusion, the process that fuels stars (and hydrogen bombs). The experiment generated an ‘ignition’ event in which more energy came out than went in: 3.15 megajoules out from 2.05 megajoules in.

Whether it can be made cheap will depend on the physics but even more on the regulation

In the words of those who did that experiment, 192 laser beams were fired into a cylinder called a ‘hohlraum’, generating a ‘bath’ of ‘soft’ X-rays that blew off the surface of a ‘peppercorn-sized capsule’, resulting in a ‘rocket-like implosion’ creating pressure and temperature ‘found only in the cores of stars and giant planets and in exploding nuclear weapons’.

Fusion energy holds enormous, if distant, promise. We know it works in stars. Its fuel is all but limitless, being made from water (some of which contains deuterium) and lithium (which can be made into tritium by........

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