|project title:||Quantized Vortices at the Interface between the A and B phases of Superfluid He3|
|project leader:||Prof. George Pickett, Dr. Richard Haley and Mr. Martin Jackson|
|access given (in days):||92|
|access used (in days):||81|
|local host:||Prof. Matti Krusius|
|home institution:||Lancaster University, Dept. of Physics|
|country of institution:||UK|
|starting date (yyyy-mm-dd):||2005-06-13|
The properties of the interface between the two superfluid phases of liquid 3He have been investigated at the University of Lancaster in the extreme low temperature limit. One of their goals is to understand the dynamics of this first order phase boundary in the zero temperature limit when dissipation approaches zero. A particular problem in this context is the interaction of the interface with quantized vortices when vortices are formed within one of the two coherent phases. One of the possibilities to answer this question is to study the interplay between vortices and the interface in rotation. Dr. Richard Haley is a lecturer and researcher from the University of Lancaster who studies the zero temperature limit of the 3He superfluids. Currently he performs measurements on the AB interface by manipulating its configuration with specially engineered time-dependent magnetic field profiles. One of his experiments is to create quantized vortex rings in the B phase and then alllow them to interact with the AB interface. At present it is not known whether a vortex ring incident on the interface is transmitted across, is reflected, or if it remains pinned on the interface. In the Low Temperature Laboratory measurements with known and more regular configurations of vorticles can be carried out in rotating samples. This insight provides useful comparison and calibration for Dr. Haley´s research in Lancaster.
Dr. Haley has participated in ongoing studies on the onset of superfluid turbulence at intermediate temperatures 0.3 - 0.6 Tc. To start turbulence, different energy barriers in series have to be overcome. Since the dissipation in vortex motion decreases rapidly with decreasing temperature, turbulence becomes more probable when one cools to lower temperatures. Dr. Haley has been examining the onset of turbulence as a function of the dissipation in vortex motion when a bunch of closely spaced vortex loops is injected in vortex-free superflow of 3He-B. The injection is performed via the Kelvin-Helmholtz instability of the AB interface in rotating flow. With this process turbulence can be started at the highest possible value of dissipation in the form of a sudden burst of turbulence. The injection mechanism, the superfluid Kelvin-Helmholtz instability of the AB interface is the foundation which has made all such later work possible. It was first reported in Phys. Rev. Lett. 89, 155301 (2002) by Blaauwgeers, Eltsov, Eska, Finne, Haley et al. and has since then led to many further collaborative publications of which the final ones are currently in preparation. Dr. Haley has also participated in the analysis of the quartz tuning fork response to quantized vortices, when these are studied in various dynamic configurations. Sizeable, easily measurable signals can be traced back to originate from vortices. However, these have turned out to be non- reproducible in ways which so far have defied a clear explanation. Since the tuning fork oscillator is a most sensitive instrument for measuring the density of quasiparticle excitations, apparently the variations in signal levels are associated with heating effects which may vary from one type of measurement to the next and also, to a smaller extent, from one day to the next. The report on this work is in preparation. The continuation was discussed at a User's Meeting end of March, 2008. Based on this collaborative work, Dr. Haley was invited to present a talk on the use of the quartz tuning fork for vortex measurements in the International Conference on Low Temperature Physics - LT25 in Amsterdam in August 2008.