Collaborative Research: Materials World Network: Collaborative Research on Simple Forms of Quantum Turbulence - Production, Decay and Visualization

经典流体中的湍流无论从理论角度还是从许多实际应用角度都是重要的和具有挑战性的。这项研究是佛罗里达大学、耶鲁大学和英国的兰开斯特大学、曼彻斯特大学和伯明翰大学之间的合作，旨在了解经典湍流如何在超流体（如液氦）中被修改，其中流动受到与角动量量子化和完全缺乏粘性相关的量子条件的严重限制。量子湍流具有依赖于温度的特性。 在低于超流体转变温度时，超流体表现为正常（类经典）流体和超流体的混合物;其中一种或两种流体都可以是湍流的，这会产生各种各样的湍流模式。如果湍流的模式能够被可视化，那么量子湍流的研究将会大大地便利。 使用微米大小的氢粒子作为示踪剂已经在其他地方开创，但该项目的研究人员正在实施使用亚稳态双原子氦分子形式的更小的粒子，这将通过激光荧光观察。 在温度略低于超流转变时，这些分子将遵循正常流体，而在更低的温度下，它们将遵循超流成分中的量子化涡旋运动。 在工作的早期阶段，研究人员将开发这种技术，以应用于分子跟踪正常流体的更容易接近的温度范围，但量子湍流的许多重要方面仍有待研究和理解。 初步实验将为低温应用铺平道路。此外，由于一个非常简单的形式的湍流可以在一个稳定移动的网格的尾流中产生，研究人员正在开发一种技术，用于在非常低的温度下移动网格通过超流氦，其中量子湍流只涉及正常流体。 由此产生的湍流将在全球范围内以两种方式进行研究：观察超流体因湍流衰减而升温的速率;以及使用离子散射来测量湍流涡旋浓度衰减的速率。拟议实验的成功取决于佛罗里达（移动网格的开发和其后能量耗散的研究）、耶鲁和曼彻斯特（可视化）、伯明翰（理论）、兰开斯特和曼彻斯特（移动网格后湍流涡旋浓度的衰减）之间密切互动合作的发展。所有实验室的学生和博士后同事将在其他实验室工作，以促进整体努力，并进一步发展每个研究人员？的能力。虽然由于低温环境，这项工作具有挑战性，但可能的回报是高的，因为对量子湍流的理解可能会提供对经典湍流的见解，而这些湍流迄今为止一直没有得到普遍的理解。

Turbulence in classical fluids is important and challenging both from a theory perspective and for many practical applications. This research, a collaboration between the University of Florida, Yale University, and the Universities of Lancaster, Manchester and Birmingham in the United Kingdom, aims to understand how classical turbulence is modified in a superfluid, such as liquid helium, in which flow is severely restricted by quantum conditions associated with the quantization of angular momentum and a complete lack of viscosity. Quantum turbulence has a character that depends on the temperature. Just below the superfluid transition temperature a superfluid behaves as a mixture of a normal (classical-like) fluid and a superfluid; either or both fluids can be turbulent, which gives rise to a rich variety of possible turbulent patterns At much lower temperatures only the superfluid component remains, exhibiting most clearly the fundamental aspects of quantum turbulence. The study of quantum turbulence would be greatly facilitated if the patterns of turbulent flow could be visualized. The use of micron-sized particles of hydrogen as tracers has been pioneered elsewhere, but the investigators in this project are implementing the use of much smaller particles in the form of metastable diatomic helium molecules, which will be observed by laser fluorescence. At temperatures somewhat below the superfluid transition such molecules are expected to follow the normal fluid, while at much lower temperatures they are expected to follow the quantized vortex motion in the superfluid component. In the earlier stages of the work the investigators will develop this technique for application in the more accessible temperature range where the molecules track the normal fluid, but where many important aspects of quantum turbulence have still to be studied and understood. The preliminary experiments will pave the way towards applications at lower temperatures. Also, since a very simple form of turbulence can be generated in the wake of a steadily moving grid, the investigators are developing techniques for moving a grid through superfluid helium at a very low temperature where the quantum turbulence involves only the normal fluid. The resulting turbulence will be studied on a global scale in two ways: observing the rate at which the superfluid heats up as a result of the decay of the turbulence; and using the scattering of ions to measure the rate at which the concentration of turbulent eddies decays. Success of the proposed experiments is dependent on the development of close interactive collaboration between Florida (development of the moving grid and study of energy dissipation behind it), Yale and Manchester (visualization), Birmingham (theory), Lancaster and Manchester (decay of the concentration of turbulent eddies behind a moving grid). Students and postdoctoral associates from all labs will work in the other labs both to promote the overall effort and further to develop each researcher?s capability. While the work is challenging because of the low temperature environment, the possible pay off is high, as an understanding of quantum turbulence may offer insights into classical turbulence which have heretofore escaped common understanding.