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Eddy Currents in the Toroidal Field Core of the Low-Aspect-Ratio Tokamak Start

R. J. Colchin

Fusion Science and Technology

Volume 29 / Number 3 / May 1996 / Pages 365-371


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START, a low-aspect-ratio tokamak located at Culham Laboratory in England, has a central copper rod that carries the whole of the toroidal field current. A small ohmic heating (OH) solenoid is wound around this central rod. The OH-driven currents in the solenoid are opposed by eddy currents in the copper rod, decreasing the volt-seconds available to drive plasma current. These eddy currents were measured and were modeled by a Laplace-transformed cylindrical heat equation. Slots in the central rod inhibit the eddy currents, increasing the effective poloidal resistance of the rod.

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