Nucleation Processes in Liquid Helium

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******NON-TECHNICAL ABSTRACT******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 soda 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. This individual investigator award supports a project to study how bubbles are formed and how to control their 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. The main aim of the project is the investigation of the effect of electrons on bubble formation. Because of the number of different experimental techniques that are involved in the research, this project provides excellent training for the graduate students working on the project.****** TECHNICAL ABSTRACT******In this research project a study will be made of electrons immersed in liquid helium. In previous research, it has been shown that 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 2nm. A new technique will be developed that will make it possible to observe the position of an electron as it moves through the liquid. The electron bubble will be expanded to a larger size for a time of around 1 microsecond and then illuminated with light from a flash lamp. In a second project, electrons that are attached to a quantized vortex line will be imaged, thus providing information about the topology of the vortex line. Because of the number of different experimental techniques that are involved in the research, this project provides excellent training for the graduate students working on the project.