stellarator is a magnetic confinement device that produces its entire twisted, confining field with intricately shaped external coils, requiring no current in the plasma itself.
The name — coined by Lyman Spitzer, who invented the concept at Princeton in 1951 — reaches for the stars, from the Latin stella: a machine to reproduce stellar fusion. Its near-neighbor and rival is the 📝Tokamak, and the difference is where the twist comes from. Both need helical field lines to confine a 📝plasma, but a tokamak makes the twist by driving a megaampere 📝plasma current through the fuel, while a stellarator builds it into the three-dimensional geometry of its coils. Giving up the current means giving up its liabilities: with no current to sustain, a stellarator can run steadily rather than in pulses, and it cannot suffer the current-driven disruptions that are the tokamak's characteristic failure.
The cost is complexity. The contorted coils are far harder to design and build than a tokamak's symmetric rings, and early stellarators leaked particles badly, which is why the field consolidated around tokamaks after 1968. Supercomputer optimization revived the concept: Germany's Wendelstein 7-X, the largest and most advanced stellarator, has sustained high-temperature plasmas for minutes at a time, and the machine now stands as the leading alternative to the tokamak within magnetic confinement fusion.