Stellarator

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A stellarator produces the twisted magnetic field needed to confine plasma entirely from external, non-planar coils, rather than from a current driven through the plasma. This removes the tokamak's dependence on plasma current and with it a family of current-driven disruptions, at the cost of a coil geometry that is far harder to design and manufacture. The concept was proposed by Lyman Spitzer at Princeton in 1951 and was for decades the underperforming alternative to the tokamak. Modern numerically optimised stellarators have narrowed that gap: Wendelstein 7-X in Greifswald reported a record triple product for long-duration plasmas sustained for 43 seconds on 22 May 2025, together with an energy turnover of 1.8 gigajoules over a 360-second discharge. No stellarator has yet operated with deuterium-tritium fuel.

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