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Nordita Astrophysics seminars

Quantum turbulence experiments: a direct look at vortex reconnections and Kelvin waves

by Enrico Fonda (New York University)

Europe/Stockholm
122:026 ()

122:026

Description
Liquid helium, as other cryogenic fluids, has a very low viscosity that allows highly turbulent flows in compact experiments. However, unlike any other fluid, when cooled below about 2.17K it becomes a superfluid, and it can flow without any friction. Vorticity in superfluids is constrained to line-like topological defects called quantized vortices. The evolution of a tangle of these vortices defines a state known as quantum turbulence. Quantum turbulence is in some ways similar to classical turbulence; for example, both show a Kolmogorov energy spectrum. However, many features of quantum turbulence, such as its velocity statistics, are distinct from classical flows. Moreover, because of the absence of viscosity, the dissipation mechanism in the zero-temperature limit must be different. Theories suggest excitation of Kelvin waves following reconnection of quantized vortices as the main dissipation mechanism. These helical waves have been recently experimentally visualized and characterized for the first time. Paper