Vortex dynamics in quantum and classical fluids

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****NON-TECHNICAL ABSTRACT****At very low temperatures, liquid helium becomes a superfluid with unusual properties and zero viscosity owing to quantum mechanical effects. One unusual aspect of superfluids is the existence of quantum vortices, sort of quantum mechanical tornadoes, that form the backbone of superfluid helium flow. This award supports a project using a unique technique to observe the formation and motion of the quantum vortices. Most of the phenomena the project will explore have not been seen before and include the motion of vortex rings and the crossing of the vortices which causes a violent snapping at the point when they touch. Undergraduate and graduate students form the heart of the project as they learn many new techniques and prepare for scientific careers. Beyond a better understanding of how superfluidity is different from normal fluids, the research serves an unusually broad need for scientific discovery in related systems involving deformation of metals, solar magnetic fields, geophysics of rotating flows, and high energy theory involving the Higgs field. **** TECHNICAL ABSTRACT **** This award supports a project to investigate and characterize the formation and dynamics of quantized vortices in superfluid helium. These studies will use a unique capability to visualize micron-sized hydrogen particles, which can be trapped by the vortices. The research focuses on studying vortex reconnection, vortex rings, thermal counterflows, rotating flows, and quantum turbulence. Furthermore, the project will explore the similarities and differences between quantum and classical turbulence in order to better understand both. Quantized vortices in superfluid helium serve as a model for a number of other systems, such that this project has the possibility to impact not only a number of sub-fields in condensed matter physics, but also astrophysics, solar physics, the geophysics of rotating flows, and high energy theory involving the Higgs field. The project broadens its impact through the involvement and training of undergraduate and graduate researchers, and through public outreach activities.