An experimental Bullard-von Kármán dynamo

International audienceInspired by a design originally proposed by Bullard ( 1955 Proc. Camb. Phil. Soc. 51 744), we report a simple experimental arrangement which generates a turbulent fluid dynamo in the laboratory. It is based on a von Karman gallium flow and it effectively models an 'alpha-omega' dynamo process, in which the alpha component is realized by external wirings, while the omega contribution fully incorporates the flow turbulence. In the dynamo state, we observe intermittent reversals of the dipole field, as well as excursions. The bifurcation develops through an 'on-off' regime