FSU researchers expand understanding of vortex scattering in superfluids - Florida State University News

FSU researchers expand understanding of vortex scattering in superfluids – Florida State University News

An illustration of a swirl tangle.  (Courtesy of Wei Guo / FAMU-FSU College of Engineering)
An illustration of a swirl tangle. (Courtesy of Wei Guo / FAMU-FSU College of Engineering)

An international team of researchers with researchers from Florida State University has developed a model that predicts the spread of vortices in so-called superfluids, work that provides new insight into the physics that control turbulence in quantum fluid systems such as superfluid neutron stars.

In a newspaper published in Physical review letters, the researchers created a model that describes the spread and velocity of tornado-like vortex tubes in superfluids. Vortex tubing is a key ingredient in turbulence, which is widely studied in classical physics. The movement of vortex tubes is relevant in a wide range of scenarios, such as the formation of hurricanes, airborne transmission of viruses and the chemical mixture in star formation. But it is poorly understood in quantum liquids.

From left, Wei Guo, an associate professor of mechanical engineering at FAMU-FSU College of Engineering, and Yuan Tang, a postdoctoral fellow at the National High Magnetic Field Laboratory, in front of an experimental setup.  (Courtesy of Wei Guo)
From left, Wei Guo, an associate professor of mechanical engineering at FAMU-FSU College of Engineering, and Yuan Tang, a postdoctoral fellow at the National High Magnetic Field Laboratory, in front of an experimental setup. (Courtesy of Wei Guo)

This work expands on a previous study that reported experimental results obtained in superfluid helium-4 within a narrow temperature range. Superfluids are liquids that can flow without resistance, and therefore without loss of kinetic energy. When they move, they form vortices that rotate indefinitely.

“By validating this model and showing that it describes the motion of vortices over a wide range of temperatures, we confirm a universal rule for this phenomenon,” said Wei Guo, an associate professor of mechanical engineering at FAMU-FSU College of Engineering. “This discovery could aid the development of advanced theoretical models of quantum fluid turbulence.”

In it previous study, Guo and his team tracked the vortex tubes that appeared in superfluid helium-4, a quantum liquid found at extremely low temperatures. In that research, the team used small particles trapped in the vortices to track their motion. They found that the vortices spread much faster than one would expect based on the seemingly random motion of the tubes. This rapid spread is called superdiffusion.

In the latest work, the researchers built a numerical model and used results from their previous study to validate the model’s accuracy by reproducing experimental results. This made it possible for them to predict how vortex tubes can form and disperse in superfluids at a wider temperature range. The simulation also provided unequivocal evidence supporting the physical mechanism proposed by the authors to explain the observed vortex superdiffusion.

Researchers strive to understand turbulence in quantum fluids for the basic research benefits as well as for possible use in practical applications, such as the manufacture of nanowires. Vortex tubes attract particles that group together in incredibly thin lines. Controlling that process enables the production of so-called nanowires, which have a thickness measured in nanometers.

“Particle scattering in turbulent flow is a very active topic in the classical turbulence field, but it has received less attention in the quantum fluid society,” said Yuan Tang, a co-author and postdoctoral fellow at the FSU headquarters National High Magnetic Field Laboratory. “Our work could stimulate more future research on particle dispersion in quantum liquids.”

Co-authors of the paper include Satoshi Yui and Makoto Tsubota from Osaka Metropolitan University, Japan, and Hiromichi Kobayashi from Keio University, Japan. This essay was chosen by Physical Review Letters as an editor’s proposal, a term for essays that are particularly important, interesting and well written.

This research was supported by the National Science Foundation and the US Department of Energy. Additional resources were provided by the National High Magnetic Field Laboratory at Florida State University, which is supported by the National Science Foundation and the State of Florida. This work was also supported by the Japan Society for the Promotion of Science.

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