Materials World Network: A Collaborative Experimental Investigation of Pure Quantum Turbulence in Superfluid 4He at Very Low Temperatures

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Turbulence in classical fluids is important and challenging both for theory and for many practical applications. This research aims to understand how classical turbulence is modified in a superfluid, inwhich flow is severely restricted by quantum conditions associated with the quantization of angular momentum and a complete lack of viscosity.At higher temperatures, superfluids exhibit "two-fluid" behavior, a normal fluid coexisting with the superfluid component in which the quantum effects are important. There is already strong evidence that at these temperatures turbulent structures on large length scales can be very similar to their classical counterparts, although dissipative processes acting on small scales are very different. It is suspectedthat a similar situation exists at very low temperatures, where the normal fluid is absent, and where simple mechanisms for the decay of the turbulence have disappeared. Our program seeks to provide experimental evidence relating to these low temperatures, at which the fundamental behavior of very pure forms of quantum turbulence ought to be observable, the turbulence being generated by either a steadily moving grid or an oscillating grid. The mechanical behavior of the oscillating grid will provide evidence about the nucleation of turbulence, and calorimetric observations with the towed grid will measure turbulent decay, which reflects not only dissipation on small scales but also the overall turbulent structure. Quantum turbulence is of great intrinsic interest, and its study could lead to a better understanding of classical turbulence.Success of the proposed experiments is dependent on the development of close interactive collaboration between Florida, Birmingham, Lancaster and Kiev. The Lancaster experimental group will do the vibrating grid work, and the Birmingham Co-Investigator will support theory development. The Kiev group will use its full chip fabrication line to develop micro-size thermal and pressure sensors for the work. Studentsand postdoctoral associates from all labs will work in the other labs to both promote the overall effort and to further develop each researcher's capability.