Scientists map microscopic roots of chaos in dusty plasma using supercomputers

Researchers at the Indian Institute of Technology (IIT) Jammu along side their colleagues at IIT Kanpur used supercomputer simulations to understand the microscopic roots of chaos in specialized state of matter called dusty plasma. The study required tracking of millions of individual particles shedding light on turbulence and opening up new avenues of research in nuclear fusion and astronomy. Basic school science teaches us that matter exists in three states, solids, liquids and gas. However, a fourth state of matter also exists, called plasma, where the smallest unit of matter, the atom is split from the electrons or negatively charged particles that orbit around its positively charged nucleus. The result is a soup of positively charged nuclei surrounded by negatively charged electrons. When tiny grains of solid dust are added to the mix, they pick up the negative charge of the electrons and interact with each other. This is called dusty plasma. When such plasma is strongly coupled, the dust grains can’t fly past each other instead behave like elastic rubber. The grains also create complex swirling patterns that turns this motion into heat, resulting in chaos or turbulence. This can be a major drawback in nuclear fusion reactors, as it prevents them from reaching temperatures necessary for energy production. Types of chaos The Indian researchers focused two types of chaos typically seen in fluids, the Kelvin-Helmholtz instability and the Rayleigh-Taylor instability. The Kelvin-Helmholtz instability is when two layers of fluids slide past each other at different speeds, much like wind blowing over the sea. In Rayleigh-Taylor instability, the two fluid layers sit on top of each other, with the heavier one sitting on top of the lighter one. The researchers turned to a molecular dynamics tool called Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) that can track every single particle in the dusty plasma and identify the moment when large swirling energy of a vortex begins to jiggle away into microscopic movements of individual particles. The researchers found that energy flow follows a mathematical pattern before setting into a thermal equilibrium and stronger the coupling between dust particles, slower is the process. In strongly coupled states, the delay in heating and mixing causes the plasma to behave like elastic turbulence. Why this study matters Traditional fluid equations like the Navier-Stokes equations do not take the graininess of matter into account and cannot accurately predict how energy is lost at the smallest scales in complex systems. Using LAMMPS simulator, the team was successful in recovering continuum behavior from the chaotic behavior of billions of individual particles, thereby helping bridge the gap between microscopic particle physics and macroscopic fluid dynamics. Bridging this gap cannot not only help solve nuclear fusion and our quest for clean energy, it also helps us understand our universe a little better. Rayleigh-Taylor instabilities are central to supernova explosions as well as volcanic eruptions and this study will help astronomers and geophysicists alike in predict how energy moves through these systems. The researchers also point out the limitations of their work, since the simulations were conducted in two-dimensions, even though most phenomena in the world are three-dimensional. Even as dusty plasma at small scales organizes itself in two dimensions, the researchers plan to carry to out 3D simulations in the future. The research findings were published in the journal Philosophical Transactions A. Get the latest in engineering, tech, space & science - delivered daily to your inbox.Ameya is a science writer based in Hyderabad, India. A Molecular Biologist at heart, he traded the micropipette to write about science during the pandemic and does not want to go back. He likes to write about genetics, microbes, technology, and public policy.