Fury: an experimental dynamo with anisotropic electrical conductivity

Abstract: We report measurements of dynamo action in a new experimental setup, named Fury, based on the use of an anisotropic electrical conductivity. It consists in a copper rotor rotating inside a copper stator, electrically connected with a thin layer of liquid metal, galinstan. Grooves have been cut in the copper so that, everywhere, electrical conductivity can be considered to be that of copper along two directions while it is zero along the third one. The configuration is efficient and dynamo action can be powered by hand. We have also used a motor with better control, enabling us to drive the rotor at specified velocity or torque functions of time. The structure of the axisymmetric magnetic field produced is found to be close to the numerical modelling using FreeFem++. The experimental dynamo behaves very nearly as expected for a kinematic dynamo, so that the threshold dynamo velocity cannot be exceeded, or only briefly. More mechanical power in the rotor rotation leads to an increase in the magnetic field intensity, the magnetic energy being proportional to the extra mechanical power beyond threshold. In the transient following a step increase of torque, magnetic and angular velocity oscillations have been observed and explained.