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

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.