Toroidal and poloidal

The two directions around a ring-shaped (toroidal) device. Toroidal means the long way round, following the ring; poloidal means the short way, around the plasma's cross-section. A tokamak's coils make a strong toroidal field, and the current in the plasma adds a weaker poloidal field; together they twist the field lines into helices, which is what keeps the plasma confined. A stellarator makes the same twist with the shape of its coils instead of a plasma current.

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concept:toroidal-poloidal

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