Phase Slip in Superfluid 4He Flow Through Microscopic Apertures

w：\awards\awards96\*.doc 9631703齐默尔曼 在过去的十年中，实验上的超流液体4He通过微米和亚微米尺寸的孔的流动已经给出了新的见解的第一次出现的耗散在流动中的临界速度。特别地，已经识别出离散的“相位滑移”事件，其被认为代表了在宇宙中单个量子涡旋的产生和演化。 超流体 目前的工作是为了提供一些额外的信息需要测试模型的创建和演变过程。此外，它将研究过渡到一个不同类型的临界速度行为，通常观察到的孔和管直径明显大于一微米。 这项工作的目的是了解超流液氦的基本流动特性。 这项研究需要接近绝对零度的温度，在那里物理系统往往表现出更简单，有时不寻常的性质。以液氦为例，它的纯度和分子结构的简单性，以及其流动中明显的有序性，使其成为检验有关流体性质和行为的基本概念的极好系统。目前的研究关注的第一次出现的混乱的流动和伴随的能量耗散的速度增加到一定水平以上，类似的不稳定性和湍流的发生在普通流体的流动的现象。这项工作的一个组成部分是在广泛的实验和研究技能的物理学研究生的培训。 ***

w:\awards\awards96\*.doc 9631703 Zimmerman Experiments during the last decade on the flow of superfluid liquid 4He through micron and submicron size apertures have given new insight into the first appearance of dissipation in the flow at the critical velocity. In particular, discrete "phase-slip" events have been identified which are thought to represent the creation and evolution of single quantum vortices in the superfluid. The present work is intended to supply some of the additional information needed to test models of the creation and evolution processes. Further, it will study the transition to a different type of critical velocity behavior that is customarily observed in apertures and tubes appreciably larger than one micron in diameter. %%% This work is directed at understanding the fundamental flow properties of superfluid liquid helium. The study requires temperatures near absolute zero, where physical systems often show simpler and sometimes unusual properties. In the case of liquid helium, its purity and molecular simplicity and the appearance of a remarkable degree of order in its flow have made it a superb system for testing fundamental ideas about the properties and behavior of fluids. The present studies concern the first appearance of disorder in the flow and the accompanying dissipation of energy as the velocity is increased above a certain level, phenomena analogous to the onset of instabilities and turbulence in the flow of ordinary fluids. An integral part of this work is the training of graduate students in physics in a broad range of experimental and research skills. ***