Nobel Prize winner in physics Richard Feynman once described turbulence as “the most important unsolved problem of classical physics”.
Classical fluids such as water and air are difficult to understand in part because it is a challenge to identify the vortices that move within those fluids. The detection and tracking of the vortex tubes can simplify the modeling of turbulence.
But this challenge comes in handy in quantum fluids, which exist at low temperatures that control their behavior when quantum mechanics – which is related to physics on the scale of atoms or sub-atomic particles.
In a new study published in the Proceedings of the National Academy of Sciences, researchers at Florida State University managed to visualize vortex tubes in a quantum fluid, findings that help researchers better understand turbulence in quantum fluids and beyond Can help in understanding.
“Our study is important not only because it broadens our understanding of turbulence in general, but also because it can benefit the study of various physical systems including vortex tubes, such as superconductors and even That neutron stars as well, ”Wei Guo said. Professor of Mechanical Engineering and Chief Investigator of Studies at FAMU-FSU Engineering College.
The research team studied superfluid helium-4, a quantum fluid that exists at extremely low temperatures and can flow forever from a narrow space without apparent friction.
Guo’s team examined tracer particles trapped in the vortex and first noticed that after the vortex tube appeared, they moved in a random pattern and, on average, rapidly moved away from their starting point. The displacement of these trapped tracers increased over time faster than a process called regular molecular diffusion – superfusion.
Analyzing what happened shows them how the vortex velocity changed over time, which is important information for statistical modeling of quantum-fluid turbulence.
“Superdiffusion has been observed in many systems such as cellular transport in biological systems and the search patterns of human predators,” Guo said. “An established interpretation of superdiffusion for things moving randomly is that they sometimes have exceptionally long displacements, known as levee flights.”
But after analyzing their data, Guo’s team concluded that the trader’s excesses in his experiment were not actually due to levy flights. Something else was happening.
“We finally found out that the superdiffusion we saw was due to the relationship between the vortex velocities,” said Yuan Tang, a postdoctoral researcher at the National High Magnetic Field Laboratory and a paper writer.
“The speed of each vortex segment initially appears to be random, but in fact, the velocity of one segment at a time was positively correlated with its velocity at the time of the next. This observation gave us some hidden general statistical Properties are allowed to be exposed. Chaotic random vortex entanglement, which can be useful in many branches of physics. ”
Unlike classical fluids, vortex tubes in superfluid helium-4 are stable and well-defined objects.
“They are essentially small tornadoes swirling in a chaotic storm but with an extremely thin hollow core,” Tang said. “You can’t see them with the naked eye, not even with the strongest microscope.”
“To solve this, we conducted our experiments in a cryogenic lab, where we added tracer particles to helium to visualize them,” added Shiran Bao, a postdoctoral researcher and a paper writer at the National High Magnetic Field Laboratory.
The researchers injected a mixture of deuterium gas and helium gas into the cold superfluid helium. When injected, deuterium gas freezes and becomes tiny ice particles, which the researchers used as liquids.
Guo said, “Just as tornadoes can suck nearby leaves in the air, our tractor can also get trapped in helium on a vortex tube.”
This visualization technique is not new and has been used by scientists in research laboratories around the world, but the success these researchers achieved was to develop a new algorithm that allowed them to distinguish tractors trapped in those vortices. The ones who were not trapped.
