Feasible homopolar dynamo with sliding liquid-metal contacts

We present a feasible homopolar dynamo design consisting of a flat, multi-arm spiral coil, which is placed above a fast-spinning metal ring and connected to the latter by sliding liquid-metal electrical contacts. Using a simple, analytically solvable axisymmetric model, we determine the optimal design of such a setup. For small contact resistance, the lowest magnetic Reynolds number, Rm?34.6, at which the dynamo can work, is attained at the optimal ratio of the outer and inner radii of the rings Ri/ Ro?0.36 and the spiral pitch angle 54.7. In a setup of two copper rings with the thickness of 3 cm, Ri=10 cm and Ro=30 cm, self-excitation of the magnetic field is expected at a critical rotation frequency around 10 Hz.