ITER, the international fusion reactor being built in France, will stand 10 stories tall, weigh three times as much as the Eiffel Tower, and cost its seven international partners $18 billion or more. The result of decades of planning, ITER will not produce fusion energy until 2027 at the earliest. And it will be decades before an ITER-like plant pumps electricity into the grid. Surely there is a quicker and cheaper route to fusion energy.

Fusion enthusiasts have a slew of schemes for achieving the starlike temperatures or crushing pressures needed to get hydrogen nuclei to come together in an energy-spawning union. Some are mainstream, such as lasers, some unorthodox. Yet the doughnut-shaped vessels called tokamaks, designed to cage a superheated plasma using magnetic fields, remain the leading fusion strategy and are the basis of ITER. Even among tokamaks, however, a nimbler alternative has emerged: a spherical tokamak.

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