Feasible homopolar dynamo with sliding liquid-metal contacts

TL;DR

This paper proposes a practical homopolar dynamo design using a flat spiral coil and liquid-metal contacts, optimized through an analytical model, predicting magnetic self-excitation at feasible rotation speeds.

Contribution

The paper introduces a new feasible homopolar dynamo design with liquid-metal contacts and provides an analytical optimization of its parameters.

Findings

Self-excitation predicted at ~10 Hz rotation frequency.

Optimal design parameters include Ri/Ro~0.36 and spiral pitch angle 54.7 degrees.

Critical magnetic Reynolds number is approximately 34.6.

Abstract

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 degrees. 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.