A Dissertation

Using frozen hydrogen particles to observe rotating and quantized flows in liquid helium Gregory P. Bewley 2006 We present a novel technique for tracing liquid helium flows, and use this technique to make observations of fluid dynamics in both the normal fluid and the superfluid phases of liquid helium. To visualize fluid motions, we create a suspension of frozen hydrogen particles with diameters on the order of one micron. We show theoretically that the hydrogen particles we generate can be used to make quantitative measurements of local flow velocities in turbulent liquid helium, and that these particles are the only ones we know of that are suitable for this purpose. In experimental work, we use the particles in normal liquid helium to examine the effect of the Coriolis force on the decay of classical turbulence using the Particle Image Velocimetry technique (PIV). We observe grid-generated turbulence in a steadily rotating frame and find that the evolution of the flow depends intimately on boundary conditions because of the production in the fluid of standing inertial wave modes of the container. Separately, we present what are very probably the first documented images of the cores of quantized vortices residing in the superfluid phase of liquid helium. Filaments we observe in the fluid are probably formed by the particle-trapping action of the quantized vortices. Although others have speculated how particles in superfluid helium could act as passive tracers of a flow, as they do in the normal fluid, our images indicate that the presence of particles in the superfluid may transform the topology of vortex tangles by stabilizing forks in the vortices.