Current Experiments

Matthew Hirsch has been investigating the escape probabilities of electron bubbles off of vortices. Electron bubbles injected into liquid helium via the tungsten tip or radioactive source can become trapped on vortices generated in the superfluid helium. Vortices can be created by a heat current in the liquid helium, rotating the cryostat, or accelerating the ions via an electric field. The trapped bubbles are then excited via a high powered infrared carbon-dioxide laser. There is a measurable probability that the electron bubble will become energetic enough to escape from the vortex.

Wei Guo has been attempting to make a movie of an electron bubble. Using a planar transducer, a sound wave can be sent through the experimental cell, which will explode all of the electron bubbles in its path. A powerful light source is synchronized with the sound pulse so that the exploding bubbles scatter the light. The resulting explosion of the electron bubble as it moves through the experimental cell is then recorded with video equipment to create a movie. Here's a sample movie taken in such an experiment: (download the movie file or click play button below)

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The bright points moving downward in the movie are electron bubbles. These bubbles are draged by the normal fluid component in liquid helium which flows downward in our experiment. Most of the bubbles move along the stream lines of the flowing liquid, while some bubbles have snake-shaped paths which are believed to be due to the bubbles being trapped on quantized vortices and sliding down the vortex lines in superfluid liquid helium.

Wanchun Wei is working on building up new apparatus to observe the so called "exotic ions".

Dafei Jin is working on the vortex imaging project and some related simulation work.

This material is based upon work supported by the National Science Foundation
under Grant No. DMR-0605355
Any opinions, findings and conclusions or recomendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF).