Experiments with tangles of quantized vortex lines in superfluid 4He in the T=0 limit
Seminar Room 1, Newton Institute
In our experiments, we can create dense ensembles of quantized vortex lines of various degrees of polarization and entanglement, and monitor either their free decay or steady state whilst forcing continuously. The superfluid is forced either by macroscopic bodies that generate large-scale vortex bundles or by microscopic particles (injected ions) that generate uncorrelated vortices. Steady net polarization can be introduced by conducting the experiment in a rotating container. The characterization of vortex tangles is done via measurements of the transport of injected ions through them. The following types of tangles will be reviewed: homogeneous random tangles (no large-scale polarization), homogeneous quasi-classical turbulence (tangles in which the dominant energy is concentrated in large-scale bundles-eddies), steadily polarized anisotropic tangles of either high or low polarization, beams of parallel vortex rings. There is no viscous dissipation in the T=0 limit; the dyn amics of individual vortex lines is conservative except for the Kelvin waves of extremely small wavelengths. The scenario and rate of the evolution of different vortex ensembles largely depend on the mutual polarization of vortioces that affects the frequency of their reconnections. Further plans to investigate the microscopic processes of the quantum cascade (Kelvin wave cascade) and visualization of individual vortex cores will be outlined.