The contribution of laboratory dynamo experiments to our understanding of the mechanism of generation of planetary magnetic fields

The magnetic fields of the Earth, Jupiter, and Saturn are now accepted as originating in a dynamo mechanism in an electrically conducting fluid region of those planets.Our extensive knowledge of the spatial and temporal variation of the geomagnetic field has been gained by observation in the recent past, and by inference from the remanent magnetisation of rocks for the distant past.The theoretical problem of predicting what sort of magnetic field can be generated by motions in a homogeneous conducting fluid is extremely intractable. In order to obtain any solution at all the problem has to be idealised until it bears little resemblance to the situation existing in planetary interiors; consequently observation and theory have little common ground.In the laboratory it is possible to construct homogeneous dynamos which, while they have a number of important differences from the mechanism which exists inside planets, nevertheless are considerably closer to reality than any theoretical model which can be shown to generate a magnetic field. Observations of the behaviour of such laboratory homogeneous self-exciting dynamos have, over the past twenty years in the Geophysics department at Newcastle University, together with theoretical predictions on one hand and palaeomagnetic observations on the other, helped towards the development of a consistent picture of both how the geomagnetic field is generated and of its morphology.This review will attempt to show the part played by experimental homogeneous dynamos in the development of the subject.