Anisotropic Formation of Quantum Turbulence Generated by a VibratingWire in Superfluid 4He

To investigate the formation of quantum turbulence in superfluid He-4, we have studied the emission of vortex rings with a ring size of larger than 38 mu m in diameter from turbulence generated by a vibrating wire. The emission rate of vortex rings from a turbulent region remains low until the beginning of high-rate emissions, suggesting that some of the vortex lines produced by thewire combine to form a vortex tangle, until an equilibrium is established between the rate of vortex line combination with the tangle and dissociation. The formation times of equilibrium turbulence are proportional to epsilon(-1.2) and epsilon(-0.)6 in the directions perpendicular and parallel to the vibrating direction of the generator, respectively, indicating the anisotropic formation of turbulence. Here, epsilon is the generation power of the turbulence. This power dependence may be associated with the characteristics of quantum turbulence with a constant energy flux.