Visualizing Quantum Turbulence in Superfluid 4He in the T=0 Limit

Abstract

An experiment has been developed for the analysis of the interactions of micron-scale fluorescent tracer particles with quantized vortices in superfluid 4He in the zero temperature limit. A method was devised in which an ultrasound transducer was coated with a layer of tracer particles which were impulsively injected into the volume of an experimental cell, thermally anchored to the mixing chamber of a dilution refrigerator. The particles were then observed as they descended through the fluid under the influence of gravity. Two classes of fluorescent microspheres were observed in the temperature range 0.14 < T < 1.2 K, both were composed of a dyed polymer. The first was a sample with uniform diameters of 6 um and a density of 1.05 g/cm^3, the second sample contained a mixture of 1-5 um diameter particles with a density of 1.3 g/cm^3. Using the particle tracking velocimetry technique, the trajectories of the particles were measured during their descent. The observed particle velocity distributions displayed Gaussian statistics with long power law tails at all temperatures, indicative of a combination of classical, viscous interactions with the normal component and non-classical interactions with quantized vortex lines. The time evolution and temperature dependencies of these distributions have been documented. An analytical technique was developed to distinguish the motion of particles strongly interacting with vortex lines from those entrained in the normal component, and a lower limit of 0.7 K has been measured for the binding of the tracer particles to vortex lines.

Date of Award	1 Aug 2024
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Andrei Golov (Supervisor) & Paul Walmsley (Supervisor)