Nucleation Processes in Liquid Helium

这是一个实验凝聚态物理项目，其目标是了解当液体处于张力状态时，气泡是如何在液氦中形成的。当一个电子被引入液氦时，它迫使液体中出现一个小空腔。这个“电子泡”的半径约为20埃。对液体施加负压会导致气泡增长，在临界压力下，气泡变得不稳定并爆炸。计划研究当电子被光学激发到不同的量子态时，引起气泡爆炸所需的压力如何变化。这些测量的结果将与已经完成的理论计算进行比较。作为实验研究的一部分，计划还测量电子不同激发态的寿命。在第二个项目中，将研究量子化涡旋对超流氦中气泡成核的影响。这项研究为研究生提供了很好的培训，他们利用最先进的仪器来研究基础物理问题，这些问题对气泡形成很重要的一些实际情况有影响。气泡在液体中的形成是许多不同过程的结果。它们可以在含有气体的液体上的压力降低时产生，例如当一罐可口可乐被打开时。当液体被加热到沸点以上时，在船的螺旋桨周围的湍流中也会形成气泡。在某些情况下，气泡的产生具有不期望的效果。例如，随着时间的推移，船舶螺旋桨附近产生的气泡会损坏螺旋桨。另一方面，气泡的产生也可以是非常有用的，如在超声波清洁器中。本研究的长期目标是研究泡沫是如何形成的，以及如何控制泡沫的形成以获得技术优势。将进行实验，以研究在一些不同的条件下，在液氦气泡的产生。之所以选择液氦进行这些实验，是因为它可以以特殊的纯度生产，因此可以控制或消除液体中杂质可能产生的影响。在本研究的下一阶段，将研究电子和涡旋对气泡形成的影响。这项研究为研究生提供了很好的培训，他们利用最先进的仪器来研究基础物理问题，这些问题对气泡形成很重要的一些实际情况有影响。

This is an experimental condensed matter physics project whose goal is to understand how bubbles are formed in liquid helium when the liquid is in a state of tension. When an electron is introduced into liquid helium, it forces open a small cavity in the liquid. This "electron bubble" has a radius of approximately 20 A. Application of a negative pressure to the liquid causes this bubble to grow, and at a critical pressure the bubble becomes unstable and explodes. It is planned to study how the pressure required to cause the explosion of the bubble changes when the electron is optically excited to different quantum states. The results of these measurements will be compared with theoretical calculations already completed. As part of the experimental study it is planned to also measure the lifetime of the different excited states of the electron. In a second project the effect of quantized vortices on the nucleation of bubbles in superfluid helium will be investigated. The research provides excellent training for graduate students who utilize state-of-the-art instrumentation to study fundamental physics problems which have implications for a number practical circumstances where bubble formation is important.%%%Bubbles form in liquid as a result of a number of different processes. They can be produced when the pressure on a liquid that contains gas is reduced, when a can of Coca Cola is opened, for example. Bubbles also form in the turbulence around the propeller of a ship, and when a liquid is heated above its boiling point. In some situations bubble production has undesirable effects. For example, over the course of time the bubbles produced near to the propeller of a ship damage the propeller. On the other hand, bubble generation can also be very useful, as in an ultrasonic cleaner. The long range goal of this research is the study of how bubbles are formed and how to control the formation for technological advantage. Experiments will be performed to investigate bubble production in liquid helium under a number of different conditions. Liquid helium is chosen for these experiments because it can be produced with exceptional purity, and so effects that might arise from impurities in the liquid can be controlled or eliminated. In the next stage of this research, the effect of electrons and vortices on bubble formation will be studied. The research provides excellent training for graduate students who utilize state-of-the-art instrumentation to study fundamental physics problems which have implications for a number practical circumstances where bubble formation is important.