The bootstrap current in stellarators

A method of calculating the bootstrap current in asymmetric devices, such as the stellarator, is developed. The features that determine the bootstrap current are the variation of the magnetic‐field strength within a magnetic surface and the rotational transform. The shape of the magnetic surfaces is shown to be irrelevant. If the fraction of trapped particles is small, the device dependence of the bootstrap current is determined by a single constant which can be calculated by integrations of the field strength along the field lines. The relative dependence of the bootstrap current on the density and the temperature gradients is the same in any device with a small fraction of trapped particles as in a large aspect ratio tokamak.

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