Dynamics of a turbulent spin-down flow inside a torus

A turbulent screw flow (with Reynolds number exceeding 10(6)) is generated by the sudden stop of a toroidal channel. The working fluid is a gallium alloy and velocity measurements are performed using a dual-axis potential probe. We describe the onset of motion, the development of strongly anisotropic fluctuations, and the final homogenization and decay of turbulence. Our observations are relevant for the relaxation of anisotropic turbulence; they are also in agreement with measurements of magnetohydrodynamic induction processes in this type of flow.