Bubbles, Ions and Vortices in Cryogenic Fluids

9731523威廉姆斯 这个低温物理项目由三部分组成。(1)利用扭转振荡器测量超流密度，研究了吸附在多孔材料中的超薄He-4膜的超流相变。这允许在超流膜的涡核直径的测量。 研究了氦-3对涡旋核尺寸的影响，以及在基体上预镀2-3层氢对涡旋结构的影响。 测量也将在一种新的多孔陶瓷材料中进行，称为MCM-41，其中材料的孔径可以在16 和100 通过改变制造工艺。本文将对氦膜中的涡旋进行理论研究，研究有限的超电流对 在Kosterlitz无涡超流转变的涡对。 (2)将进行从声学捕获在低温液体如氮气和氧气中的气泡的声致发光的搜索，并将使用激光散射研究气泡的振荡动力学。 低温液体具有纯净和惰性的优点。 它们在紫外区也比水更透明，大部分声致发光能量都是在紫外区发射的。(3)在液氦中，通过向液体中注入电子也会产生气泡，形成足够大的多电子气泡，从而被声场捕获。将测量作为电子数的函数的气泡半径，以及气泡的振荡动力学。 这个低温物理项目由三个部分组成。(1)本文将研究液氦薄膜的超流性质，重点是了解液体中的量子化涡旋流线如何使无摩擦超流停止。测量液氦中超流部分的大小将使涡旋结构的大小得以确定。 一种新型的陶瓷材料将被用作氦膜的基底，其孔径可以在约16 和100 . 将开展理论研究，为以下方面提供框架： 解释实验结果。 这项工作 在高温超导体中，量子化的涡旋磁通线在超导转变附近被激发。这些线的作用是使电子的无摩擦流动停止。(2)将进行从低温液体如氮气和氧气中的气泡中寻找声致发光的研究， 将使用激光散射来研究气泡表面的振荡运动。导致水中振荡气泡产生100皮秒光脉冲的机制仍然不清楚，重要的是要找到发生这种现象的其他液体。稀有气体低温液体具有非常纯净和惰性的重要优点，并且在光谱的紫外区域中比水更透明，其中大部分光从气泡发射。(3)在液氦中，通过向液体中注入电子也会产生气泡，形成内部含有数百万电子的小气泡。将测量作为电子数的函数的气泡的半径，以及气泡表面的振荡运动。 ***

9731523 Williams This low temperature physics project is composed of three components. (1) The superfluid phase transition of very thin He-4 films adsorbed in porous materials will be studied, using a torsion oscillator to measure the superfluid density. This allows a measurement of the vortex core diameter in the superfluid films. The increase of in the vortex core size with added He-3 will be studied, and also the effect on the vortex structure of pre-plating the substrate with 2-3 atomic layers of hydrogen. Measurements will also be undertaken in a new porous ceramic material, known as MCM-41, where the pore size of the material can be varied between 16 and 100 by changing the fabrication process. Theoretical studies of the vortices in helium films will be carried out, investigating the effect of a finite supercurrent on the vortex pairs at the Kosterlitz-Thouless superfluid transition. (2) A search for sonoluminescence from bubbles acoustically trapped in cryogenic liquids such as nitrogen and oxygen will be undertaken, and the oscillation dynamics of the bubbles will be studied using laser scattering. The cryogenic liquids have the advantages of being pure and inert. They are also more transparent than water in the ultraviolet region, where most of the sonoluminescent energy is emitted. (3) Bubbles will also be created in liquid helium by injecting electrons into the liquid, forming multi-electron bubbles large enough to become trapped in the acoustic fields. The bubble radius as function of the electron number will be measured, and also the oscillation dynamics of the bubble. %%% This low temperature physics project is composed of three components. (1) The superfluid properties of liquid helium films will be studied, with the emphasis on understanding how quantized vortex flow line in the liquid can bring the frictionless superfluid flow to a halt. Measurem ents of the fraction of the liquid helium that is superfluid will allow the size of the vortex structures to be determined. A new type of ceramic materials will be employed as a substrate for the helium films, one whose pore size can be varied between about 16 and 100 . Theoretical studies will be carried out to provide a framework for interpreting the experimental results. This work has applications to the High-Tc superconductors, where it is just now being understood that quantized vortex flux lines are excited near the superconducting transition. These lines have the effect of bringing to a halt the frictionless flow of the electrons. (2) A search for sonoluminescence from bubbles in cryogenic liquids such as nitrogen and oxygen will be undertaken, and the oscillatory motion of the surface of the bubbles will be studied using laser light scattering. The mechanism that results in the 100 picosecond bursts of light from oscillating bubbles in water is still not understood, and it is important to find other liquids where the phenomenon occurs. The noble-gas cryogenic liquid have the important advantages that they are very pure and inert, and are more transparent than water in the ultraviolet region of the spectrum where most of the light is emitted from the bubbles. (3) Bubbles will also be created in liquid helium by injecting electrons into the liquid, forming small bubbles with up to several million electrons inside. The radius of the bubble as a function of the number of electron will be measured, and also the oscillatory motion of the bubble surface. ***